AN  ANALYSIS  OF  THE  EFFECTS  OF  SELECTION 


Bt  a.  h.  sturtevant 


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AN  ANALYSIS  OF  THE  EFFECTS  OF  SELECTION 


By  A.  H.  STURTEVANT 


Published  by  the  Carnegie  Institi 

Washington,  19 


THIS  BOOK  IS  DUE  ON  THE  DATE 
INDICATED  BELOW  AND  IS  SUB- 
JECT TO  AN  OVERDUE  FINE  AS 
POSTED  AT  THE  CIRCULATION 
DESK. 


CARNEGIE  INSTITUTION  OF  WASHINGTON 
Publication  No.  264 


V  -     »     • 


PRESS  OF  GIBSON  BROTHERS 
WASHINGTON,  D.  C. 


STURTEVANT 


PLATE  1 


■    ■ 


1.  Dichaet  male  (5-bristled)       2.  Extended  female.     3.  Wild-type  female. 

(Drawings  by  Miss  E.  M.  Wallace.) 


ANANALYSIS  OF  THE  EFFECTS  OF  SELECTION.1 


INTRODUCTORY  SUMMARY. 

The  present  paper  describes  a  series  of  experiments  aimed  a1  de- 
termining  the  causes  of  the  variability  in  bristle  number  observed  in 
Dich«t,   a   mutant   race   of   Drosophila  melanogaster   (ampelopki 
These  experiments  are  discussed  under  several  headings,  as  follows: 

(a)  Selection  of  plus  and  of  minus  variants  was  carried  out.  Both 
plus  and  minus  lines  were  obtained  and  were  used  in  the  further  ex- 
periments. 

(b)  A  plus  line  and  a  minus  line  were  crossed,  and  an  increase  in 
variability  was  observed  in  F2. 

(c)  Linkage  tests  were  made,  and  by  this  means  it  was  demon- 
strated that  modifying  genes  were  present  in  the  selected  lines. 

(d)  Evidence  against  the  hypothesis  of  contamination  of  allelo- 
morphs was  obtained. 

(e)  This  evidence,  and  that  obtained  by  other  investigators,  is  then 
utilized  in  a  general  discussion  of  the  selection  problem,  and  of  the 
hypothesis  of  contamination  of  genes.  The  conclusions  are  drawn 
that  selection  is  usually  effective  only  in  isolating  genetic  diflferen- 
already  present;  and  that  genes  are  relatively  stable,  not  being  con- 
taminated in  heterozygotes,  and  mutating  only  very  rarely. 

DICH/ET. 

The  mutant  character  known  as  Dichset  was  discovered  by  Dr. 
C.  B.  Bridges,  July  3,  1915.  In  an  experiment  involving  the  sex- 
linked  characters  sable,  forked,  and  cleft  there  appeared  a  single 
female  that  had  wings  extended  and  bent  backwards  near  the  base, 
like  those  of  the  mutant  bent  (Muller,  19146).  In  addition  it  was 
observed  that  this  female  had  only  2  dorso-central  bristles,  instead 
of  the  4  usually  present.  When  mated  to  a  male  having  the  mutant 
character  eyeless,  this  female  produced  48  normal  offspring  and  46 
"Dichset,"  thus  showing  the  character  to  be  dominant. 

Bridges's  unpublished  data  show  that  the  Dichaet  gene  is  in  the  third 
chromosome,  approximately  5  units  to  the  left  of  junk. 

The  data  published  by  Muller  (1916)  give  the  locus  as  9.7  from  Bepia 
(the  locus  farthest  to  the  left  of  those  as  yet  discovered),  and  11.0 
from  spineless,  on  the  right.     My  own  (unpublished)  data  give: 

Sepia  Dich*t,  ^-  =  14.9  p.  ct.       Dichaet  spineless,  -—  -   13.1  p.  ct 

13b9  • ° ' 


U  am  indebted  to  Mr.  J.  W.  Gowen  for  much  advice  and  assistance  in  eonneotion  with  the 
statistical  treatment  of  the  present  problem.  He  has  done  a  pari  of  the  actual  calculation*, 
but  is  not  responsible  for  any  arithmetical  slips,  as  I  ha%-e  myself  done  all  tbfl  Checktaf. 


AN  ANALYSIS   OF   THE   EFFECT   OF   SELECTION. 


The  averages,  roughly  weighted  according  to  number  of  individuals, 
are:  sepia  Dichset,  13;  Dichset  spineless,  12.  This  agrees  with  the 
data  of  Bridges  on  the  position  of  Dichset  with  reference  to  pink,  since 
that  locus  is  about  8  to  the  left  of  spineless. 

Bridges  also  found  that  homozygous  Dichsets  are  not  produced. 
The  gene,  like  that  of  the  yellow  mouse,  acts  as  a  lethal  when  homozy- 
gous. The  result  is  that  when  Dichsets  are  mated  together  they 
produce  two  heterozygous  Dichsets  to  one  not-Dichset.  This  dis- 
covery has  been  verified  by  the  experiments  described  in  this  paper, 
and  by  other  experiments  carried  out  by  Muller  and  by  the  author. 

Table  1. 


Figs.  1  and  2. — Two  types  of  bristle  distribution 
in  Dichsets — a  "3"  and  a  "7."  Small  post-alars  are 
present  in  fig.  2.    These  are  never  counted  in  the  totals. 


Culture 
No. 

No.  of  bristles. 

Total. 

3 
1 

4 

9 
23 

9 
32 

7 

5 

20 
29 
11 
22 
15 

6 

27 
30 
11 
13 
3 

881 
882 
883 
900 
2715 

58 
83 
31 
67 
25 

1 

80 

97 

84 

262 

2  and  7  bristles  have  also  been  ob- 
served in  unselected  stocks. 


As  shown  in  plate  1,  fig.  1,  the  wings  of  Dichset  flies  are  held  out  from 
the  body  and  are  bent  back  near  the  base.  The  number  of  dorso- 
central  bristles  (on  the  dorsum  of  the  thorax)  on  the  original  female 
was  2  instead  of  4,  as  is  usually  the  case  in  the  normal  fly  (plate  1, 
figs.  1  and  3).    This  has  since  been  found  to  be  a  variable  character. 

The  number  of  dorso-centrals  varies  from  0  to  4,  and  sometimes 
one  or  more  of  the  scutellars  may  be  missing.  In  addition,  the  an- 
terior post-alars  above  and  just  behind  the  wing-base  are  reduced  or 
absent.  Plate  1,  figure  1,  and  text-figures  1  and  2  show  some  common 
types.  The  work  reported  in  this  paper  has  consisted  in  selecting  for  a 
high  and  for  a  low  total  of  scutellar  and  dorso-central  bristles.  Counts 
from  five  unselected  cultures  gave  the  results  as  shown  in  table  1. 

The  normal  flies  occasionally  show  variations  in  bristle  number, 
but  these  are  much  rarer  than  in  the  case  of  Dichset.  MacDowell 
(1915)  has  given  some  data  on  the  frequency  of  these  variations,  and 
has  also  reported  on  very  extensive  selection  experiments  with  them 
(1915,  1917).     These  experiments  will  be  referred  to  below. 

I  have  made  bristle  counts  on  a  few  unselected  not-Dichset  stocks, 
with  the  results  shown  in  table  2. 

The  normal  flies  have  8  dorso-central  and  scutellar  bristles  in  most 
cases,  while  the  Dichsets  range  from  1  to  8.  But  the  8-bristled  Dichsets 
are  still  distinguishable  from  normals,  even  when  their  wings  are  not 


AN    ANALYSIS    OF   THE    EFFECT    OF    SELECTION. 


unfolded  enough  so  that  they  can  be  separated  on  that  basis.  This 
is  because  the  anterior  pair  of  dorso-centrals  never,  so  far  as  I  have 
observed,  becomes  as  large  as  the  corresponding  pair  in  normal  flies. 
The  anterior  post-alars  are  also  reduced  in  8-bristled  Dichaets.     This 


Table  2. 


Stock. 

6 

7 

8 

9 

10 

Total. 

9 

d" 

9 

& 

9 

d" 

9 

c? 

9 

cf 

Wild: 

Falmouth,  Massachusetts. 

Berkeley,  California 

Mitchell,  South  Dakota. . . 
Amity,  Oregon 

0 
0 
0 
0 
0 
0 
0 
0 
0 
0 

0 
0 
0 
0 
0 
0 
0 
0 
0 
0 

0 
0 
0 
0 
0 

1 

0 
0 
0 
0 

1 

0 
0 
0 
0 
5 
0 
0 
0 
0 

186 
95 

226 
59 
16 

103 
26 
80 

114 
74 

118 
104 
213 
51 
21 
99 
38 
92 
67 
77 

11 
0 
4 
1 
0 
1 
0 
0 
0 
2 

2 
0 
1 
1 
1 
0 
0 
0 
0 
0 

0 
0 
0 
0 
0 
0 
0 
0 
0 
0 

0 
0 
0 
0 
0 
0 
0 
0 
0 
0 

318 
199 
444 
112 

38 
209 

64 
172 
181 
153 

Sydney,  Australia 

Black 

White 

1 

separability  is  a  matter  of  some  importance,  since,  because  of  the 
lethal  effect  of  Dichset,  any  Dichaet  culture  may  produce  normal 
flies.  However,  the  spread  wings  can  be  and  are  used  for  the  separa- 
tion in  all  but  the  rather  rare  instances  of  failure  to  expand  properly. 

SEXUAL  DIMORPHISM. 

Calculations  show  that  there  is  a  slight  but  significant  sexual  di- 
morphism in  bristle  number  in  the  Dichset  races.  Random  selection 
of  plus  and  of  minus  selected  cultures  gave  the  totals  shown  in  table  3. 

Table  3. 


Bristle  number. 

Total. 

1 

2 

3 

4 

5 

6 

7 

8 

Plus  9 . . . . 

4 
25 
17 

177 

490 

436 

1,517 

1,190 

668 
684 
712 
615 

1,702 

1,527 

424 

332 

81 

53 

7 

2 

6 

8 

2,951 
2,736 
2,682 
2,356 

Plus  cT 

Minus  9  •  ■ 
Minus  cf . . 

1 

3 

5 

39 

These  distributions  give  the  statistical  constants  shown  in  table  4. 

The  first  three  columns  show  that  there  is  a  slight  difference  in  the 
means,  the  females  being  higher  in  both  cases.  In  the  case  of  the  plus 
series  the  difference  is  doubtfully  significant;  in  the  minus  series  it  is 
larger  and  certainly  significant.     The  last  column  gives  the  chance 


6  AN   ANALYSIS   OF   THE    EFFECT    OF    SELECTION. 

that  differences  as  great  as  those  observed  between  the  two  distribu- 
tions are  due  to  random  sampling.  These  values  were  obtained  by 
Pearson's  x2  method  (Pearson,  1911).  This  column  makes  it  quite 
certain  that  there  is  a  significant  sexual  dimorphism  in  both  series, 
and  also  brings  out  again  the  fact  that  the  dimorphism  is  greater  in 
the  minus  series. 

Table  4. 


9  Mean. 

cT  Mean. 

Difference. 

P 

Plus 
Minus. . . 

5.468±0.010 
4.583±    .010 

5.428±0.010 
4.436±    .012 

0.041±0.014 
.147±    .016 

0.0001 
.0000000  + 

Because  of  the  information  given  by  this  table  it  has  seemed  de- 
sirable to  present  the  data  for  males  and  females  separately.  This 
has  been  done  in  the  Appendix;  but  since  the  dimorphism  is  slight, 
the  data  have  been  lumped  in  the  statistical  treatment  given  in  the 
body  of  the  paper.  The  data  in  the  Appendix  make  it  possible  to  re- 
calculate the  constants  separately  if  it  should  seem  desirable  to  do  so. 

EFFECTS  OF  ENVIRONMENT. 

In  any  selection  experiment  it  is  obviously  very  important  to  have 
some  information  regarding  the  influence  of  environmental  conditions 
on  the  variable  character  used.  If  the  observed  variations  in  the 
character  are  largely  due  to  environmental  causes,  it  should  be  very 
difficult  to  accomplish  much  by  selection;  but  if  the  environment 
plays  little  part  in  causing  variability,  selection  should  be  very  effective 
in  isolating  different  types,  and  on  the  multiple-factor  view  variability 
should  show  a  marked  decrease  after  a  few  generations  of  inbreeding. 

In  the  case  of  Dichset,  it  has  been  observed  that  as  cultures  grow 
older  the  flies  frequently  have  fewer  bristles.  In  such  cultures  it  is 
usually  observed  that  the  later  flies  are  also  smaller  and  that  the  food 
conditions  in  the  bottle  have  become  unfavorable.  It  is,  therefore, 
essential  in  such  experiments  that  conditions  be  made  as  nearly  uni- 
form as  practicable. 

The  data  in  table  5  show  that  under  ordinary  conditions  there  is 
considerable  environmental  effect.  Eight  pairs  from  the  regular  series 
were  transferred  to  second  bottles,  after  staying  the  usual  period  in 
the  first  one.  Offspring  were  thus  obtained  with  identical  pedigrees 
and  differing  only  in  that  they  were  reared  in  separate  bottles.  No 
attempt  has  been  made  to  make  conditions  different  in  the  two  bottles, 
which  constitute  a  random  sample  of  the  conditions  under  which  the 
experiments  were  carried  out.  Table  5  shows  the  results  obtained. 
(The  actual  data  are  in  the  Appendix;  the  first  three  columns  of  the 


AN   ANALYSIS   OF   THE   EFFECT   OF   SELECTION. 


table  will  enable  the  reader  to  find  them.)  The  last  three  columns 
give  the  results  of  an  application  of  the  x2  test  to  the  data.  The  last 
column,  headed  P,  gives  the  chance  (1.0  representing  certainty)  that 
deviations  from  identity  as  great  as  those  observed  could  have  re- 
sulted from  random  sampling.  It  follows  that  in  at  least  three  cases 
(the  fifth,  sixth,  and  seventh)  the  results  given  by  the  two  broods  were 
significantly  different. 

Table  5. — First  and  Second  Broods  from  Same  Parents. 


Culture  Nos. 

Series. 

Gener- 
ations 
mother 
inbred. 

X2 

n' 

P 

First 
brood. 

Second 
brood. 

1,907 
1,908 
1,912 
1,924 
2,074 
2,078 
2,087 
2,475 

1,996 
1,997 
1,998 
1,999 
2,140 
2,141 
2,142 
2,518 

1331 

1002  rev 

4 

6 

7 

7 

9 

11 

11 

J18 

3.74 

5.60 

2.10 

6.05 

22.09 

16.81 

19.80 

5.22 

3 
5 

4 
5 
4 
4 
5 
3 

0.16 
.23 
.55 
.19 

.0001 
.001 
.0005 
.075 

1002 

1002 

900 

Test  of  crossbr.  plus . 
864 

Test  of  1002 

^is  and  F17  were  mass  cultures  in  this  case. 

There  is  one  possible  source  of  error  in  these  data:  It  has  been 
shown  by  Bridges  (1915)  that  the  amount  of  crossing  over  in  the  sec- 
ond chromosome  of  Drosophila  varies  with  the  age  of  the  female. 
My  own  unpublished  data  show  that  this  is  also  true  for  the  third 
chromosome.  In  the  present  case,  if  the  female  parents  of  the  flies 
observed  were  heterozygous  for  many  modifying  factors,  such  a 
change  in  linkage  might  result  in  the  production  of  genetically  differ- 
ent first  and  second  broods.  However,  the  female  parents  in  these 
cultures  were  in  every  case  from  at  least  four  generations  of  brother- 
sister  inbreeding  (see  table  5,  column  4)1  and  in  the  significant  cases 
for  9  and  11  generations.  It  is  therefore  very  unlikely  that  they  were 
heterozygous  for  many  modifying  factors.  The  two  broods  from 
these  females  must,  then,  be  of  the  same  genetic  constitution,  and  the 
differences  between  them  can  only  be  due  to  environmental  causes. 
It  follows  that  in  the  experiments  recorded  below  a  significant  part 
of  the  variability  is  not  genetic,  but  environmental. 

METHODS. 

With  very  few  exceptions,  the  flies  recorded  in  this  paper  were  bred 
from  pairs,  and  in  pint  milk  bottles.  The  food  used  was  ripe  un- 
cooked banana,  fermented  in  a  stock  yeast-culture  for  from  12  to  48 

^hree  cases  in  which  the  female  parents  were  hybrids  have  been  discarded  (see  2091-2143, 
3064-3116,  3066-3118  pairs  in  Appendix). 


8 


AN   ANALYSIS   OF   THE   EFFECT   OF   SELECTION. 


hours  (usually  about  24  hours) .  Paper  toweling  was  added  to  absorb 
surplus  moisture. 

The  experiments  were  begun  in  New  York  City  in  February  1916, 
and  were  carried  on  there  until  the  middle  of  June,  when  the  material 
was  moved  to  Woods  Hole,  Massachusetts,  and  continued  there  until 
the  end  of  September.  All  these  flies  were  kept  at  room  temperature. 
The  work  was  resumed  in  November,  in  New  York,  and  continued 
until  the  middle  of  May  1917.  During  these  last  six  months  the 
flies  were  reared  in  a  heated  case  that  was  regulated  by  a  thermostat, 
so  that  the  minimum  temperature  was  about  24°,  the  maximum  being 
about  26°,  except  when  room  temperature  went  a  few  degrees  higher, 
as  occasionally  happened.  It  is  to  be  noted  that  the  constant-tempera- 
ture series  run  more  evenly  (see  especially  1002  line),  thus  suggesting 
that  temperature  influences  bristle  number. 

In  order  that  the  data  presented  in  the  Appendix  may  be  correlated 
with  this  information,  if  it  seems  desirable  to  do  so,  the  following 
table  is  presented.  Each  culture  received  a  serial  number  at  the  time 
the  parents  were  mated,  and  these  numbers  run  consecutively  through- 
out all  the  author's  recent  experiments  (on  other  problems  as  well  as 
selection).  These  serial  numbers  are  recorded  in  the  Appendix. 
Therefore,  it  is  possible  to  fix  approximately  the  date  on  which  a  cul- 
ture was  made  up,  if  we  know  the  date  on  which  a  culture  with  a  simi- 
lar number  was  made  up.  The  dates  of  all  cultures  are  noted  on  the 
record  sheets,  but  it  has  seemed  hardly  necessary  to  present  more  than 
the  following  "landmarks." 

Table  6. 


Culture. 

Date. 

Culture. 

Date. 

Culture. 

Date. 

884 
1006 
1100 
1150 
1301 
1401 

Feb.  3,  1916 
Mar.  24,  1916 
Apr.  16,  1916 
Apr.  22,  1916 
May  15,  1916 
May  28,  1916 

1507 
1617 
1830 
2000 
2250 

June  7, 1916 
June  23,  1916 
July  14,  1916 
Aug.  1,  1916 
Aug.  28,  1916 

2389 
2423 
2601 
2950 
3078 

Sept.  16,  1916 
Nov.  18,  1916 
Jan.  13,  1917 
Mar.  17,  1917 
Apr.  15,  1917 

SELECTION. 

If  the  variations  observed  in  the  Dichset  character  are  due  to  modi- 
fication of  the  Dicha^t  gene  itself,  selection  should  be  as  effective  in 
inbred  stocks  as  in  any  other  kinds.  If  multiple  factors  are  responsible 
for  the  variations,  the  method  of  breeding  should  affect  the  result. 
If  a  stock  is  closely  inbred  while  being  selected,  it  will  soon  become 
fairly  uniform,  so  that  selection  should  be  effective  for  only  a  com- 
paratively short  time.  But  if  a  strain  is  subjected  to  some  crossing 
it  will  become  uniform  more  slowly,  so  that  selection  should  be  effective 


AN   ANALYSIS   OF   THE   EFFECT   OF   SELECTION. 


9 


longer.  Moreover,  there  is  a  chance  of  combining  more  of  the  desired 
modifiers  in  the  same  individual  when  crossing  is  done,  so  that  this 
method  might  produce  more  extreme  results  than  the  inbreeding 
method.  However,  each  time  a  cross  is  made  some  of  what  has  been 
gained  may  be  hidden  by  dominants  in  the  other  stock;  therefore 
progress  might  sometimes  be  slower. 

Accordingly,  in  these  experiments  parallel  series  have  been  carried 
on.  In  one  set  selection  has  been  accompanied  by  continuous  brother- 
sister  matings;  in  the  other,  frequent  crosses  have  been  made  between 
individuals  more  or  less  closely  related.  The  same  method  has  been 
followed  in  both  the  plus  and  the  minus  selected  lines.  The  four 
series  will  be  considered  in  order:  (1)  inbred  plus;  (2)  crossbred  plus; 
(3)  inbred  minus;  (4)  crossbred  minus. 

INBRED  PLUS  SERIES. 

Two  main  lines  of  this  series  have  been  carried  on.  A  few  cultures 
have  been  made  from  other  sources,  but  none  of  these  are  sufficiently 
extensive  so  that  we  need  follow  their  histories  here. 

864  Line. 

Culture  864,  from  which  this  line  arose,  was  produced  by  a  female 

D'       r0 

of  the  constitution      .   ,  s     from  culture  847,  and  two  males  from 

pvsske  r0 

the  sepia,  spineless,  kidney,  sooty,  rough  stock;  847  was  the  result  of 

mating  four  peach,  spineless,  kidney,  sooty,  rough  males  from  stock  to  a 

D'r0 

female  of  the  constitution  — = — .     This  female 

P%e 

was  descended  from  the  Dichset,  ebony,  peach, 

spineless,  kidney,  sooty,  rough,  and  other  stocks. 

Her  pedigree  is  not  now  traceable  in  detail. 

At  the  time  culture  864  was  counted,  the  scu- 
tellar  bristles  were  not  observed.  The  dorso- 
central  bristles  were  recorded  on  30  flies,  as 
shown  in  table  7. 

The  3  (almost  certainly  a  7,  according  to  the  system  later  adopted), 
a  male,  was  mated  to  a  2  (6)  female  to  produce  culture  893.  For  the 
details  of  the  remainder  of  the  pedigree  see  Appendix. 

In  the  accompanying  tables  and  curves  the  offspring  of  culture 
893,  above,  are  considered  Fi.  Table  8  gives  the  data  for  this  line 
summarized  by  generations.  In  this  and  the  following  tables,  n  is 
the  number  of  individuals  in  the  generation,  M  is  the  mean  bristle- 
number  of  the  generation,  a  is  the  standard  deviation,  r  is  the  parent- 
offspring  correlation,  and  is  recorded  in  the  generation  to  which  the 
offspring  belong.  Diff.  M.  is  the  mean  bristle-number  of  the  off- 
spring minus  the  mean  bristle-number  of   their  parents,  weighted 


Table  7. 


Dorso- 
centrala. 

Offspring. 

0 
1 
2 
3 

Total 

12 
8 
9 

1 

30 

10 


AN    ANALYSIS    OF   THE    EFFECT    OF    SELECTION. 


according  to  number  of  offspring,  and  is  also  recorded  in  the  offspring 
generation.  In  the  calculation  of  r,  the  parental  grades  are  taken  as 
the  average  grades  of  the  two  parents.  When  r  is  not  given,  it  is  not 
capable  of  calculation,  for  the  reason  that  all  parental  pairs  in  that 
generation  were  of  the  same  average  grade.  The  correlation  coeffi- 
cients given  here  are  of  doubtful  significance,  though  many  of  them 
are  several  times  their  probable  errors.     These  probable  errors,  like 

Table  8. — 864,  Inbred  Plus  Line. 


Generation. 

n 

M 

a 

r 

Diff.  M. 

Fi. 

113 
121 
73 
260 
149 
120 
510 
461 
154 
159 
232 
624 
353 
175 

5.672±0.048 
5.331±    .049 
5.822±    .031 
4.904±    .036 
5.228±    .043 
5.450±    .044 
5.190±    .025 
5.475±    .023 
5.643±    .034 
4.956=>=    .051 
5.224±    .039 
5. 272=±=    .025 
5.787±    .024 
6.080=*=    .026 

0.762  ±0.034 
.804=>=    .035 
.396=t=    .022 
.868=<=    .026 
.771=i=    .030 
.705=i=    .031 
.835±    .018 
.738=*=    .016 
.621=*=    .024 
.960=*=    .036 
.867=*=    .027 
.937=t=    .018 
.667===    .017 
.506=*=    .018 

-0.828 
-1.179 

-  .178 
-1.016 

-  .772 

-  .550 

-  .810 

-  .514 

-  .458 
- 1 . 044 

-  .901 

-  .728 

-  .762 

-  .300 

F2 

F3 

F4 

Fk 

Fb 

F7 

F8 

+0.105±0.031 
+    .002±    .054 

F9 

Fio 

Fi, 

Fi2 

Fi4 

-    .011±    .044 

-    .070±    .036 
+    .133±    .050 

3,504 

Reversed  Selection. 

Fi, 

F,2 

Fl3 

33 
49 
62 

144 

5.152±0.102 
5.327===    .092 
5.710=>=    .052 

0.869  ±0.072 
.956±    .065 
.606±    .037 

+0.652 
+  1.329 
+  1.710 

others  of  their  kind,  are  intended  only  to  give  the  magnitude  of  the 
error  likely  to  arise  from  the  fact  that  one  is  dealing  with  a  sample  of 
limited  size — the  error  of  random  sampling.  But  in  the  present  case 
the  correlation  coefficient  is  intended  to  measure  the  similarity  be- 
tween the  somatic  appearance  and  the  genetic  possibilities  of  the 
parent  individuals.  It  is  known  that  this  similarity  does  not  amount 
to  identity,  and  that  it  may  be  modified  in  individual  cases  bv  en- 
vironmental causes.  Since  in  any  given  case  we  are  dealing  with  a 
rather  small  number  of  parent  individuals,  but  a  large  number  of  off- 
spring individuals,  the  selection  of  one  or  two  parents  whose  somatic 
appearance  differs  widely  from  their  genetic  possibility  will  throw 
the  resulting  correlation  coefficient  far  off;  but  the  large  number  of 
offspring-  will  keep  the  probable  error  down.  If,  instead  of  entering 
each  offspring  individual  in  the  correlation  table  separately,  we  enter 
only  the  mean  grade  of  the  offspring  of  each  parent  pair,  we  get  what 
is  perhaps  a  more  reasonable  probable  error.     But  this  method  fails 


AN   ANALYSIS   OF   THE    EFFECT    OF    SELECTION. 


11 


to  weight  the  results  from  different  parents  according  to  the  number 

(and  therefore  reliability)   of  their  offspring.     In  the  present    <•• 
also,  it  gives  an  extremely  large  probable  error,  and  probably  giv< 
less  accurate  value  for  the  coefficient  itself.     The  usual  method  has 
accordingly  been  followed,  but  little  reliance  is  to  be  placed  on  the 
biological  significance  of  the  results  obtained.     Hence  in  the  follow- 
ing discussion  the  correlation  coefficients  will  be  largely  ignored. 


Fig.  3. — Means  and  standard  deviations  for  864  inbred  plus  line.  The  gener- 
ation number  is  given  on  the  abscissa;  bristle  number  on  the  ordinate. 
The  dotted  lines  represent  reverse  selection. 


The  values  for  M  and  a  in  the  864  line  are  plotted  in  figure  3. 
Selection  has  apparently  affected  this  line  hardly  at  all.  This  is  per- 
haps because  in  the  early  generations  so  few  individuals  were  bred 
from.  Reversed  selection  (dotted  line  in  curve)  was  ineffective  in 
the  eleventh  to  thirteenth  generations,  thus  indicating  again  that  at 
that  stage  at  least  the  line  was  not  capable  of  modification  through 
selection.1 

1002  Line. 

The  second  inbred  plus  line  is  descended  from  culture  1002.     The 

D' 

female  in  this  culture  was  of  the  constitution  — t~t~  and  the  four 

sesske  r0 

males  were  from  the  peach,  spineless,   kidney,   sooty,   rough   stock. 

xThe  fact  that  the  signs  of  the  differences  between  the  means  are  reversed  when  selection  is 
reversed  is  due  simply  to  the  fact  that  the  parents  Beleote  1  arc  now  below  the  mean  of  the  line, 
instead  of  above  it.  The  difference  between  the  means,  likr  the  correlation  coefficient,  is  of 
slight  significance  when  the  number  of  parent  individuals  is  as  small  as  in  these  experiments,  and 
for  the  same  reasons. 


12  AN   ANALYSIS   OF   THE   EFFECT   OF   SELECTION. 

The  female  was  from  culture  916,  which  contained  a  sepia,  spineless, 

D' 

kidney,  sooty,  rough  male,  and  a  female .    This  female  was  the 

offspring  of  a  Dichset  from  stock  and  of  a  fly  from  culture  869  (q.  v. 
below,  in  the  pedigrees  of  900  and  crossbred  minus  lines) .  No  bristle 
counts  are  available  from  culture  1002,  except  those  of  the  pair  (6X6) 
selected  to  produce  culture  1072,  the  Fi  of  this  line. 

After  this  line  had  been  inbred  and  selected  for  11  generations,  a 
pair  of  7-bristled  flies  were  taken  from  2389,  and  their  descendants  were 
bred  in  mass  cultures,  unselected  Dicha^ts  being  mated  together,  for 
about  2  generations.  The  line  was  then  re-established  by  selecting 
pairs  from  this  stock  and  was  inbred  for  8  generations  more. 

The  data  and  curves  for  this  line  are  given  in  table  9  and  figure  4. 


123456789      10      11  123456 

Fig.  4. — Means  and  standard  deviations  for  1002  inbred  plus  line. 

Here  selection  was  perhaps  effective  for  a  few  generations.  Ref- 
erence to  the  Appendix  will  indicate  that  this  effectiveness  was  prob- 
ably due  in  large  part  to  the  gradual  elimination  of  the  descendants 
of  one  of  the  F2  pairs  (1158),  which  were  on  the  average  of  slightly 
lower  grade  than  those  of  the  other  F2  pair  (1150) .  It  is  to  be  observed 
that  both  of  the  apparently  successful  reversed-selection  series  were 
made  with  descendants  of  the  former  branch  of  the  family. 

The  eighth  to  eleventh  generations  of  this  line  and  the  contempo- 
rary eleventh  to  fourteenth  of  the  864  line  gave  very  similar  results 
as  to  the  means  and  standard  deviations.  We  shall  see  below  (p.  19) 
reason  for  believing  that  the  two  lines  were  of  very  similar  constitution 
at  this  period.  The  gradual  rise  of  the  means  and  fall  of  the  standard 
deviations  is  probably  of  environmental  rather  than  genetic  origin. 


AN   ANALYSIS   OF   THE   EFFECT   OF   SELECTION. 


13 


The  "new"  series,  which  was  carried  on  at  a  constant  temperature, 
shows  remarkably  little  fluctuation.  Of  the  two  reversed-selection 
series,  one  suggests  a  positive  result,  but  was  not  carried  on  long 

Table  9.— 1002,  Inbred  Plus  Line. 


Generation. 


Fi 

F2 

F3 

F4 

FB 

F8 

F7 

F8 

F9 

Fio.  .  .  . 
Fn.... 

New  set 
Fi.. 
F«.. 
F,.. 
F4.. 
F5.. 
F... 
F7.. 
F8.. 


114 
231 
446 
1,199 
1,142 
632 
283 
584 
373 
269 
133 

5,406 

167 

447 

377 

79 

73 

128 

92 

79 

1,442 


M 


5.070=*= 
5.052=*= 
5.473=*= 
5.126=*= 
.658=*= 
.389=*= 
.675=*= 
.202=*= 
5.507=*= 
5.952=*= 
6.158=*= 


0.051 
.039 
.025 
.018 
.014 
.022 
.027 
.023 
.027 
.018 
.026 


5. 850=*=  0.021 

5.978=*=  .011 

5.889=*=  .020 

5.886=*=  .031 

5.904=*=  .046 

5.969=*=  .026 

5.935=*=  .027 

5.937=*=  .045 


0.815=*=0.036 

.886=*=  .028 

.784=*=  .018 

.922=*=  .013 

.720=*=  .010 

.853=*=  .015 

.683=*=  .019 

.826=*=  .016 

.763=*=  .019 

.450=*=  .013 

.456=*=  .018 


0.362=*=0.014 

.340=*=  .008 

.563=*=  .014 

.422=*=  .022 

.578=*=  .032 

.429=*=  .018 

.381=*=  .019 

.534=*=  .031 


+  .157=*=0.031 

+  .153=*=  .019 

-  .024=*=  .020 
+  .381=*=  .024 

-  .305=*=  .036 
+  .431=*=  .022 
+  .205=*=  .033 
+  .115=*=  .040 

-  .025=*=  .058 


1-0.038=*=0.046 
-  .009=*=  .032 
+  .048=*=  .034 
1  +  .123=*=  .042 
i_  .062=*=  .072 
l-    .031=*=    .039 


Reversed  Selection. 


F6 

F6 

Ft 

F8 

Ft 

New  set 

F4... 

FB... 

F4... 


62 
46 
68 
23 
125 

49 
13 
99 


485 


5.339±0 

.085 

4.652=*= 

.089 

4.147=*= 

.062 

4.739=*= 

.119 

4.680=*= 

.060 

5.898±0 

.046 

6.000=*= 

.000 

5.707=*= 

.041 

0.989  ±0.060 
.890=*=  .063 
.753=*=  .044 
.845=*=  .084 
.993=*=    .042 

0.463=*=  0.032 
.000=*=  .000 
.573=*=    .028 


Did.  M. 


-0.930 

-  .948 

-  .661 
-1.113 

-  .397 
-1.029 
-1.127 
-1.122 

-  .690 

-  .128 

-  .477 


4-0.087 

-  .668 
-1.114 

-  .096 

-1.165 

-  .063 


+  1.339 
+  .652 
+  .147 
+  1.239 
+  1.180 

+0.898 
+    .500 


'Includes  reversed  selection,  that  is,  not  included  in  the  remainder  of  these  data. 


enough  to  be  significant,  and  the  other  was  clearly  without  effect. 
The  line  was  now  presumably  uniform,  and  not  capable  of  modifica- 
tion through  further  selection. 

CROSSBRED  PLUS  SERIES. 

The  material  for  this  series  came  from  the  following  sources:     Cul- 
tures 902,  926,  1006,  1081  of  the  864  inbred  plus  line;  culture  1072  of 


14 


AN    ANALYSIS    OF   THE    EFFECT    OF    SELECTION. 


the  1002  inbred  plus  line;  2  individuals  (in  cultures  937  and  1074) 
from  the  Dichset  stock;  culture  1004,  which  was  made  up  from  exactly 
the  same  sources  as  1002  (see  above),  and  differed  from  that  culture 
only  in  that  a  single  male  was  used. 

This  material  was  mated  in  various  ways,  but  brother-sister  matings 
were  practised  infrequently,  and  then  (see  Appendix)  not  often  in 
successive  generations.  All  the  cultures  in  this  set  were  descended 
from  the  864  inbred  line;  and  the  " generation"  of  each  culture  has 
been  taken  as  the  greatest  number  of  generations  from  864  shown  by 
any  line  of  the  ancestry  of  that  culture.  This  method  is  somewhat 
misleading,  since  in  every  case  the  " generation"  thus  given  is  higher 
than  the  average  number  of  selected  generations,  and  still  higher  than 
the  average  number  of  crossbred  selected  generations  in  the  pedigree. 
For  example,  the  first  culture  in  the  series,  937,  is  recorded  as  F3, 
since  the  father  came  from  the  F2  generation  of  the  864  line;  but  the 
mother  was  an  unselected  individual  from  the  Dichset  stock.  Cul- 
ture 1074  is  recorded  as  F5,  though  the  father  was  unselected  and  the 
mother  was  from  the  inbred  864  line.  Culture  1254  is  recorded  as 
F7,  though  one  parent  belonged  to  F5,  and  the  only  grandparent 
not  an  F4  came  from  1074,  above.  This  method  of  grouping  the  data 
has  been  adopted  because  it  is  convenient  to  handle,  and  because  it 


Table  10. — Crossbred  Plus  Series. 


Generation. 

n 

M 

a 

r 

Diff.  M. 

F3 

F4 

F5 

F6 

53 
417 

£12 
1,031 
1,006 

877 
388 
236 

5. 283  ±0.079 
5.211=*=    .028 
5.489=*=    .018 
5.790=*=    .012 
5.733=*=    .015 
5.616=*=    .018 
5.840=t=    .024 
5.822=*=    .026 

0.856±0.056 
.849=*=    .020 
.779=*=    .013 
.599=*=    .008 
.717=*=    .011 
.790=*=    .013 
.711=*=    .017 
.591=*=    .018 

-1.217 

-  .719 

-  .643 

-  .772 

-  .891 
-1.423 
-1.120 
-1.589 

+0.156=*=  0.023 
+    .027=*=    .021 

-  .023=*=    .021 

-  .086=*=    .023 

-  .147=*=    .034 

-  .196=*=    .042 

F7 

F8 

F9 

Fio 

4,820 

is  desirable  for  purposes  of  comparison  and  computation  to  have  the 
generations  expressed  in  whole  numbers.  The  errors  involved  all 
tend  to  make  it  appear  that  selection  has  been  applied  longer  than  is 
actually  the  case,  and  this  should  be  borne  in  mind  when  studying 
table  10  and  the  curve  (fig.  5)  for  this  series.  The  pedigrees  may  be 
traced  from  the  data  in  the  Appendix,  if  anyone  cares  to  make  a  differ- 
ent classification. 

Selection  has  apparently  been  successful  in  raising  the  mean  of  this 
series;  but  this  conclusion  is  not  certainly  correct,  because  of  the  en- 
vironmental possibilities  discussed  above. 


AN   ANALYSIS    OF   THE    EFFECT    OF    SELECTION. 


L5 


INBRED  MINUS  SERIES. 


As  in  the  case  of  the  inbred  plus  series,  two  lines  wen-  carried  on 
here.  One  of  these  was  not  kept  long;  but  its  history  is  given  here, 
chiefly  because  it  was  used  in  producing  the  crossbred  minus  line. 


900  Line. 


Culture  900  produced  Dichset  flies  as  shown  in  table    11 
This  culture  was  produced  by  mating  a  male 
from  the  sepia,  spineless,  kidney,  sooty,  rough 


Table  11. 


stock  to  a  female  of  the  constitution 


D1 


sfe 


that 


Bristles. 

Offspring. 

4 
5 
6 

Total 

32 
22 
13 

67 

was  obtained  by  inbreeding  a  pair  of  flies  from 
869  (see  pedigree  of  1002  inbred  plus  line). 
869  was  produced  by  a  male  from  the  sepia, 
spineless,  kidney,  sooty,  rough  stock  and  a  fe- 
male from  854,  which  came  from  839  (9)  and  840  (d").  840  also 
enters  into  the  pedigree  of  the  868  line,  below.  839  and  840  were 
sister  pairs,  the  males  coming  from  the  sepia,  spineless,  kidney,  Booty, 
rough  stock,  and  the  females  being  Fi  hybrids  of  the  sepia,  peach, 
ebony,  and  Dichset  stocks. 


i"    n 


Fig.  5. 


Fio.  5. — Means  and  standard  deviations  for  crossbred  plus  line. 
Fig.  6. — Means  and  standard  deviations  for  900  inbred  minus  line. 


Table  12  and  the  curve  (fig.  6)  for  this  line  are  arranged  in  the  same 
way  as  those  for  the  inbred  plus  lines. 


16 


AN   ANALYSIS   OF   THE   EFFECT   OF   SELECTION. 


The  effectiveness  of  selection  is  doubtful,  but  the  line  runs  con- 
sistently lower  than  the  three  plus  lines,  and  reversed  selection  was 
perhaps  effective. 

Table  12. — 900,  Inbred  Minus  Line. 


Generation. 

n 

M 

CT 

r 

Diff.  M. 

Fi 

130 
204 
256 
194 
243 
103 
148 
69 
271 
762 
340 

4.769±0.045 
4.603=*=    .038 
4.578±    .032 
4.959=t=    .040 
5.124±    .037 
4.660±    .077 
5.000±    .044 
4.826±    .070 
4.576±    .031 
4.555±    .019 
5.141±    .031 

0.771±0.032 
.794=t    .027 
.767±    .023 
.818±    .029 
.847±    .026 

1.146±    .054 
.797±    .031 
.867±    .050 
.740=i=    .022 
.769±    .014 
.849±    .022 

+0.769 
+  .603 
+  .976 
+  1.000 
+  1.255 
+  .660 
+  1.986 
-  .420 
+  .644 
+  .654 
+  1.340 

F2 

F3 

+ 
+ 

.021± 
.155± 
.032=*= 

.042 
.048 
.043 

F4 

F6 

F6 

F7 

+ 
+ 

.103=*= 
.159=1= 
.005=== 
.011=±= 
.142± 

.055 
.079 
.041 
.024 
.036 

F„ 

F9 

Fn 

2,720 

Reversed  Selection. 

F3 

68 
71 
98 

4.897===  0.062 
5.451±      .062 
5.194±      .032 

0.750=*=  0.044 
.728±      .044 
.488=t=      .023 

-1.103 

-  .549 

-  .806 

F4 

F6 

237 

Table  13. 


868  Minus  Line. 

This  line  is  descended  from  culture  868,  which  was  produced  by  a 
sepia,  Dichset,  ebony-sooty  female  from  856  and  a  rough  male  from 
852;  856  was  the  result  of  mating  a  stock  sepia,  spineless,  kidney, 
sooty,  rough  male  to  a  Dichset  ebony-sooty 
female  from  840  (q.  v.  above,  in  pedigree  of 
900  line).  852  was  a  descendant  of  the  peach, 
spineless,  kidney,  sooty,  rough,  and  peach- 
ebony  stocks,  and  (although  it  did  not  trace  to 
the  Dichset  stock)  of  the  same  original  cultures 
as  864,  the  ancestor  of  the  first  inbred  plus  line 
(see  above). 

The  offspring  of  868  itself  were  classified  for 
dorso-central  bristles,  as  shown  in  table  13. 

The  data  for  the  succeeding  generations  are  given  in  table  14  and 
figure  7. 

The  numbers  of  individuals  and  of  generations  are  rather  small, 
for  the  reason  that  the  line  was  not  very  vigorous,  and  finally  died 
out  in  spite  of  all  attempts  to  preserve  it.  It  gave  the  lowest  means 
of  any  line  so  far  discussed.  Reversed  selection  was  apparently  suc- 
cessful. 


Dorso- 
centrals. 

Offspring. 

0 
1 
2 
3 
4 

Total      ,  ,  , 

25 

17 
9 
0 
0 

51 

#*« 


igh 


AN    ANALYSIS    OF   THE   EFFECT   OF    SELECTION 
Table  14.— S6S,  Inbred  Minus  Line. 


17 


Generation. 

n 

M 

tx 

F, 

74 
109 
193 
68 
84 
22 

550 

4. 432  ±0.070 
4.688=*=    .053 
4.104=*=    .042 
3.765=1=    .063 
4.286=1=    .053 
4.228===    .106 

0.888=«=0.049 
.820*  .037 
.834=*=  .029 
.768=*=  .044 
.716=*=  .037 
.736=*=    .075 

F2 

F3 

F4 

F6 

F6 

Reversed  Selection. 

F« 

112 
225 

337 

4.732±0.055 
4.862=*=    .039 

0.856=*=0.038 
.866=*=    .027 

F6 

CROSSBRED  MINUS  SERIES. 

The  following  cultures  furnished  the  material  for  this  series : 

Cultures  920,  1063,  1073,  1082  of  the  900  minus  line. 

Cultures  935,  936,  1047  of  the  868  minus  line. 

Culture  942,  made  up  by  mating  together  two  4-bristled  Dichaets 
from  912,  which  in  turn  was  the  result  of  mating  a  sepia,  spineless, 
kidney,  sooty,  rough  male  to  a  female  from  a  daughter  culture  of 
869  (see  pedigree  of  900  line). 

Culture  949,  made  up  by  mating  a  female  of  the  constitution  - 

(from  the  cultures  of  Mr.  J.  W.  Gowen)  to  a  male  from  culture  916 
(see  pedigree  of  1002  line). 

All  the  cultures  in  this  series  traced  to  868,  and  the  "generation" 
given  is  the  greatest  number  of  generations  from  868,  which  is  thus 
the  standard  for  this  line,  just  as  864  was  for  the  crossbred  plus  series. 

Table  15  and  figure  8  give  the  results  for  the  series.  Here  again, 
the  effectiveness  of  selection  is  suggested,  but  is  doubtful.  The  means, 
however,  are  lower  than  in  any  other  series  except  the  868  line,  and 
that  line  entered  very  largely  into  the  make-up  of  this  one. 

Speck  Minus  or  1331  Line. 

In  connection  with  certain  experiments  to  be  described  below  it 
became  desirable  to  have  a  minus  line  that  should  be  recessive  for  some 
second  chromosome  character.  Accordingly  culture  1331  was  made 
up  by  mating  a  4  female  from  1168,  F6  of  the  crossbred  minus  Beri 
to  a  speck  male.1  The  line  was  then  inbred,  in  pairs,  brother  to  sister, 
minus  selected,  and  gradually  made  homozygous  for  speck,  sepia,  and 
rough. 


18 


AN    ANALYSIS   OF  THE   EFFECT   OF   SELECTION. 


12       3       4        5       6 


4       5      6       7       8       9      10     11     12 


Fig.  7. 


Fig.  8. 


Fig.  7. — Means  and  standard  deviations  for  868  inbred  minus  line. 
Fig.  8. — Means  and  standard  deviations  for  crossbred  minus  line. 


Table  15. — Crossbred  Minus  Series. 


Generation. 

n 

M 

a 

r 

Diff.  M. 

Ft   . 

323 

688 

1,022 

1,473 

1,503 

401 

265 

245 

177 

4.523±0.028 
4.297=4=    .020 
4.667=4=    .017 
4.357=*=    .013 
4.522=*=    .014 
4.354=4=    .025 
4.083===    .026 
4.073=*=    .030 
4.475=*=    .039 

0.753=*=0.020 
.786=4=    .014 
.829±    .012 
.735=4=    .009 
.788=4=    .010 
.730=4=    .017 
.621=4=    .018 
.666=4=    .021 
.767=4=    .027 

+0.523 
+   .711 
+  1.280 
+   .558 
+1.055 
+    .742 
+   .511 
+1.008 
+  1.334 

F6 

+0.070=4=0.026 

-  .048=*=    .021 

-  .151=4=    .017 
+   .026=4=    .016 

-  .142=4=    .033 

-  .107===    .041 
+    .230=4=    .041 

-  .191=4=    .049 

F6 

F7 

F8 

F9 

Fio 

F,i 

6,097 

JFrom  Ft  of  the  inbred  speck  line  described  later. 


Table  16  and  figure  9  show  the  result.  The  break  after  F8  represents 
the  same  treatment  as  that  given  to  the  1002  line  (p.  10) — i.  e.,  two 
generations  of  unselected  mass  cultures. 

This  line  gives  perhaps  the  clearest  evidence  of  the  effectiveness  of 
selection  that  we  have  yet  observed.  Reversed  selection  begun  in 
F2  was  apparently  also  successful.  Finally,  the  line  after  F2  gives 
consistently  lower  means  than  any  other  here  recorded. 


AN   ANALYSIS   OF   THE   EFFECT   OF   SELECTION. 


19 


12345678  12345 

Fig.  9. — Means  and  standard  deviations  for  speck  (1331)  minus  line. 


Table  16. — 1331  (Speck),  Minus  Line. 


Genera- 
tion. 

n 

M 

a 

r 

Diff.  M. 

Fi 

125 
298 
395 
377 
307 
169 
159 
27 

21 
36 
99 
163 
16 

4. 464  =±=0.044 
4.688=*=    .031 
4.187±    .026 
4.141=±=    .017 
4.072=*=    .016 
3.982=*=    .022 
3.943=*=    .019 
4.333=*=    .071 

4. 000=*=  0.076 
4.417=*=    .072 
4.081=*=    .045 
3.951=*=    .031 
3.188=*=    .167 

0.733  ±0.031 
.790=*=    .022 
.767=*=    .018 
.495=*=    .012 
.425=*=    .012 
.414=*=    .015 
.341=*=    .013 
.547=*=    .050 

0.535  ±0.048 
.638=*=    .051 
.629=*=    .031 
.584=*=    .028 
.948=*=    .118 

F2.. 
F,.. 
F4.. 
F6.. 
F«.. 
F7.. 
F8.. 

+0.132=*=  0.039 
a+   .170=*=    .028 
1+    .224=*=    .030 
J+    .023=*=    .037 

-  .184=*=    .050 

-  .014=*=    .053 

+0.896 

»-    .435 

l-    .134 

J+   .303 

+   .304 

+    .399 

+  1.333 

+  1.000 
+    .417 
+    .0M 
2+   .295 
+    .188 

New  set: 
Fi.... 
F2.... 
F3.... 
F«.... 
F«.... 

0.000=*=  0.147 

2+   .136=*=    .051 

2,192 

Revei 

ised  Selection. 

F3 

161 
91 
21 

4. 429=*=  0.035 
4.451=*=    .052 
4.143=*=    .114 

0.603=*=  0.025 
.743=*=    .037 
.773=*=    .0S0 

F« 

F6 

273 

includes  data  from  reversed  selection. 

'Includes  culture  2625,  a  mating  of  6  X6.     This  culture  is  not  included  in  the  other  columns. 


20  AN   ANALYSIS    OF   THE    EFFECT    OF    SELECTION. 

GENERAL  RESULTS  OF  SELECTION  EXPERIMENTS. 

In  every  case  the  selected  lines  showed  means  that  differed  from  the 
mean  of  unselected  Dichsets  in  the  direction  in  which  selection  had 
been  carried  on.  Owing  to  the  apparently  large  environmental  influ- 
ence on  bristle  number,  it  is  in  most  cases  difficult  to  be  sure  how  this 
result  was  brought  about,  or,  rather,  at  what  stage  in  the  process. 

In  the  case  of  the  1331  (speck)  minus  line,  however,  the  change  seems 
to  have  been  effected  fairly  rapidly  at  first,  and  slowly,  if  at  all,  later 
on.  In  the  case  of  the  1002  line  there  was  probably  no  effect  in  the 
later  generations.  Reversed  selection  was  uniformly  successful  if 
begun  in  the  early  generations,  but  not  usually  so  at  later  stages. 
These  are  the  results  that  would  be  expected  on  the  view  that  modify- 
ing genes  are  involved. 

It  is  to  be  observed  in  the  case  of  the  plus  lines  that  the  means  vary 
inversely  as  the  standard  deviations — that  is,  that  the  two  curves 
are  much  like  mirror  images.  In  the  minus  lines  the  two  quantities 
usually  vary  together,  giving  curves  that  are  nearly  parallel.  These 
relations  hold  surprisingly  closely  for  many  of  the  curves,  especially 
those  of  the  plus  lines.  They  are  due  to  the  fact  that  a  change  in  the 
mean  is  almost  always  brought  about  by  an  elimination  or  great  de- 
crease in  the  number  of  individuals  at  one  extreme  of  the  population 
rather  than  by  a  marked  change  in  the  position  of  the  mode  or  of  the 
other  extreme.  This  is  strongly  in  favor  of  the  view  that  selection 
has  been  effective  in  eliminating  "unfavorable"  combinations  rather 
than  in  producing  entirely  new  types. 

The  relation  between  the  crossbred  and  inbred  series  is  too  much 
obscured  to  repay  detailed  analysis.  Evidently  such  experiments 
with  this  character  would  have  to  be  carried  out  under  carefully  con- 
trolled environmental  conditions  before  they  could  have  any  great 
significance. 

CROSS  OF  TWO  INBRED  PLUS  LINES. 

Since  the  two  inbred  plus  lines,  864  and  1002,  came  from  slightly 
different  sources  (see  above),  and  were  kept  separate  while  being  plus 
selected,  it  seemed  possible  that  different  plus  modifiers  had  been 
isolated  in  the  two  lines.  If  this  were  the  case,  crossing  them  should 
result  in  increasing  the  variability  in  F2,  and  the  parent -offspring 
correlation  when  the  F2  individuals  were  bred  to  produce  F3.  The 
F2  population  should  contain  genetically  unlike  individuals,  and 
should  yield  to  selection  in  either  direction.  As  a  matter  of  fact,  no 
such  result  was  obtained. 

Table  17  gives  the  result  of  the  experiment.  The  1941  set  is  per- 
haps the  clearest  case,  so  we  may  consider  it  alone.  The  parents  of 
1941  came  from  1763  (Fj0  of  the  864  line)  and  1788  (F7  of  the  1002 
line).     As  table  17  and  figure  10  show,  the  standard  deviation  in  F2 


AN   ANALYSIS   OF   THE    EFFECT    OF    SELECTION, 


21 


Table  17. — Inbred  Plus  Lines  Crossed. 


Generation. 


Pi. 

F2. 


n 


192 
689 


M 


5.365= 
5.374= 


;0.041 
=    .022 


().s_M  ±0.029 
.817=*=    .015 


1941  Set  Alone. 


Fi 

F2 

[Total . 
F3     Plus.. 

[Minus. 

Total . 

F4  J  Plus. . 

[Minus. 


42 
279 
605 
395 
210 
303 
270 

33 


1,789 


5.500=*=0.0S0 


5.233=*= 
5.783=*= 
5.767=*= 
5.814=*= 
6.116=*= 
6.144=*= 
5.879=*= 


.034 
.018 
.023 
.031 
.020 
.022 
.069 


0.764  ±0.056 

.843=*= 

.024 

.666=*= 

.013 

.677=*= 

.016 

.649=*= 

.022 

.533=*= 

.014 

.526=*= 

.015 

.588=*= 

.019 

1  —  0.27S=t=0  (0  1 

-    .036=*= 


+    .131=*=    .038 


1  Does  not  include  culture  2054,  in  which  the  mother  was  not-Dichaet. 
10  11 


Fig.  10. — Means  and  standard  deviations  for  cross  of  two  inbred  plua  lini 
Fig.  11. — Means  and  standard   deviations  for  cross  of   1002  inbred   pltu 
and  speck  (1331)  minus  lines. 

was  nearly  the  same  as  that  in  Fb  the  F2-F3  and  F3-F4  parent-offspring 

correlations  were  not  significantly  different  from  0,  and  the  means  of 
the  plus  and  minus  selected  series  in  F3  and  F4  were  practically  identi- 
cal. This  constitutes  practically  a  proof  thai  the  two  lines  did  not 
differ  with  respect  to  modifying  genes.  The  result,  while  surprising, 
is  by  no  means  highly  improbable  on  the  multiple-factor  view.     The 


22 


AN  ANALYSIS   OF  THE   EFFECT    OF   SELECTION. 


two  lines  both  came  in  large  part  from  the  sepia,  spineless,  kidney, 
sooty,  rough,  and  peach,  spineless,  kidney,  sooty,  rough  stocks,  and 
therefore  selection  presumably  had  similar  material  to  work  with  in 
both  cases.  That  the  result  was  the  same  is,  then,  only  a  somewhat 
unexpected  coincidence.  It  may  be  pointed  out  that  the  identity  of 
the  two  lines  is  borne  out  by  their  very  similar  behavior  after  the 
seventh  and  tenth  generations,  respectively.     (See  figs.  3  and  4,  above.) 

CROSS  OF  PLUS  AND  MINUS  LINE. 

When  two  races  that  differ  in  quantitative  characters  are  crossed, 
the  usual  result  is  an  increased  variability  in  F2  and  an  increased 
F2-F3  parent-offspring  correlation.  This  result  was  obtained  in  the 
present  case,  as  is  shown  by  table  18  and  figures  11  and  12,  which 
give  the  data  for  a  cross  of  the  1002  plus  and  1331  minus  lines. 

Table  18. — Cross  of  Inbred  Plus  and  Inbred  Minus  Lines. 


Generation. 

n 

M 

<r 

r 

Fi 

F2 

F3 

lF, 

53 

369 

1,133 

1,078 

5.679=4=0.049 
4.694=4=    .037 
5.524=4=    .016 
5.492=4=    .013 

0.542=4=0.035 

1.052=4=    .026 

.787=4=    .oil 

.610=4=    .009 

+0.193=4=0.034 
+    .258=4=    .019 
+    .330=4=    .019 

1,555 

'Calculated  after  elimination  of  aberrant  culture  3077. 


Such  a  result  is  capable  of  explanation  in  either  of  two  ways.  It 
may  be  due  to  the  segregation  of  modifying  factors,  or  it  may  be  due 
to  contamination  of  unlike  allelomorphs  in  the  Fi  individuals. 

The  contamination  hypothesis  presents  some  unusual  features  in 
the  present  case;  for  the  Fi  Dichsets  were  not  heterozygous  for  one 
plus  Dichset  gene  and  one  minus  one;  homozygous  Dichsets  always  die. 
Half  of  them  had  one  plus  selected  Dichset  gene  and  one  minus  selected 
normal  allelomorph  of  Dichset  (i.  e.,  not-Dichset) ,  the  other  half  had 
one  minus  selected  Dichset  and  one  plus  selected  not-Dichset.  Both 
not-Dichsets,  when  homozygous,  give  for  the  most  part  8-bristled 
flies,  which  are  more  "plus"  than  any  Dichset  race.  Nevertheless, 
on  the  contamination  view,  each  must  contaminate  its  mate  in  the  Fi 
fly,  in  the  direction  in  which  it  has  been  selected.  Even  the  minus 
selected  not-Dichset,  that  makes  for  8  bristles,  must  contaminate  the 
plus  selected  Dichset,  that  makes  for  6  bristles,  in  such  a  way  that 
the  resulting  Dichset  gene  makes  for  only  4  or  5  bristles.  That  is, 
"plusness"  or  "minusness"  and  "  Dichsetness "  must  be  separable, 
and  a  degree  of  "minusness"  that  affects  the  result  produced  by  a 
not-Dichset  gene  only  very  slightly  must  nevertheless  be  capable  of 


AN   ANALYSIS   OF   THE   EFFECT   OF   SELECTION. 


23 


transference  to  a  Dichset  gene  and  must  materially  affect  the  result 
produced  by  that  Dichset  gene. 

The  hypothesis  that  modifying  genes  are  responsible  for  the  result 
meets  with  no  such  complications. 

LOCATION  OF  MODIFYING  GENES. 


60 


40 


.-,., 


60 


40 


20- 


The  selection  experiments  recorded 
above  have  demonstrated  that  Dichset 
lines  exist  that  are  genetically  different 
with  respect  to  bristle  number.  The 
cross  between  the  1002  plus  line  and 
1331  minus  line  showed  that  there  is  an 
increase  in  variability  in  F2  when  two 
such  lines  are  crossed.  Both  these  facts 
are  consistent  with  the  view  that  modi- 
fying genes,  other  than  the  Dichset  gene 
itself,  have  influenced  the  bristle  num- 
ber of  Dichset  flies.  But  it  would  also 
be  possible  to  interpret  the  result  as 
due  to  variations  in  the  Dichset  gene  it- 
self, and  to  contamination  of  that  gene 
in  crosses.     (See  above.) 

It  has  been  pointed  out  by  Muller  and 
Altenburg  (Morgan,  Sturtevant,  Muller 
and  Bridges,  1915,  p.  191),  by  Dexter 
(1914),  and  by  Muller  (1917)  that  there 
is  a  method  of  distinguishing  between 
these  two  possibilities.  The  truncate 
race  of  Drosophila  with  which  Muller 
and  Altenburg  worked  is  characterized 
by  shortened  "truncated"  wings, 
race  does  not  breed  true  for  the  trun- 
cate character,  but  the  percentage  of 
truncates  produced  and  the  degree  of 
truncation  shown  are  both  capable  of 
modification  by  selection.  Muller  and 
Altenburg  showed  that  this  race  contains  a  mutant  gene  in  the  second 
chromosome  that  is  primarily  responsible  for  the  truncate  character. 
By  means  of  linkage  experiments  involving  readily  classifiable  mutant 
characters  they  were  able  also  to  show  that  there  are  modifying  fact  i  ore 
for  the  truncate  character  in  the  first  and  in  the  third  chromosomes. 
Furthermore,  when  the  stock  was  by  special  methods  kept  uniform  in 
constitution  with  respect  to  the  truncate  gene  itself  and  with  respect  to 
these  modifiers,  selection  was  without  effect.  In  this  way  the  genetic 
variability  of  the  race  was  shown  to  be  due  to  modifying  factor-. 


40 

^~~L 

20 

f. 

r-T 

, 

1 


y 


The  Fia-  12.— Results  of  crossing  1002  in- 
bred plus  and  speck  (1331)  minus 
lines.  The  Pi  curves  represent  the 
last  few  generations  of  each  parent 
race.  All  four  curve.-;  fcre  radooed  to 
the  percentage  basis;  the  ordinatea 
represent  percentages  and  the  ab- 
scissae bristle  numbers. 


24  AN   ANALYSIS   OF   THE   EFFECT   OF   SELECTION. 

Dexter  (1914)  showed  by  similar  methods  that  the  chief  gene  for 
the  variable  character  beaded  is  in  the  third  chromosome,  and  that 
there  is  a  modifier  in  the  second  chromosome.  These  results  have 
been  verified  by  Muller  (1917). 

In  making  such  tests  for  modifying  factors  it  is  very  desirable  that 
the  test  stocks,  as  well  as  the  selected  stocks  that  are  to  be  tested, 
should  be  homogeneous  for  modifying  genes.  This  is  desirable  in 
order  that  the  tests  may  be  repeated,  and  in  order  that  results  ob- 
tained with  different  stocks  may  be  compared.  It  was  for  this  pur- 
pose that  the  speck  minus,  or  1331,  line  of  this  paper  was  obtained. 
(See  above  for  history  of  this  line.)  This  line,  in  the  later  generations, 
was  homozygous  for  the  recessive  mutants  speck  (chromosome  II) 
and  sepia  and  rough  (chromosome  III).  Since  it  had  been  inbred 
and  minus  selected  for  several  generations,  it  was  probably  uniform 
in  constitution  with  respect  to  modifiers.  Since  the  other  selected 
lines  also  became  homozygous  for  rough  in  later  generations,  it  was 
desirable  to  have  a  uniform  not-rough  line.  For  this  purpose  a  pair 
was  taken  from  the  speck  stock,  wild  type  in  other  characters.  From 
this  pair  a  line  was  established,  and  continued  by  strict  brother-sister 
pair  matings,  in  order  to  obtain  a  stock  nearly  or  quite  homozygous 
for  all  its  genes.  This  material  is  designated  "speck  stock."  All 
individuals  from  it  that  were  used  for  test  purposes  came  from  8  or 
more  successive  brother-sister  matings.1 

Sex-linked  modifiers  would  become  apparent  in  Fi  when  two  races 
were  crossed,  since  the  males  from  reciprocal  crosses  would  differ  and 
each  type  would  resemble  the  maternal  race.  There  is  no  clear  evi- 
dence of  the  existence  of  such  modifiers  in  this  experiment,  so  the  sex 
chromosome  will  be  ignored  in  the  discussion  that  follows. 

The  method  used  for  detecting  second-chromosome  modifiers  is 
as  follows:  Two  lines  are  crossed,  one  of  which  contains  speck,  the 
other  not;  one  or  both  have  Dichset  (fig.  13).  The  Fi  Dichaets  are 
then  heterozygous  for  speck,  and  for  any  second-chromosome 
modifiers  in  which  the  two  lines  were  different.  If  an  Fi  male  is  now 
mated  to  a  speck  not-Dicha^t  female,  there  will  be  no  crossing  over 
between  speck  and  the  modifiers.  Therefore  the  not-speck  Dichsets 
produced  will  receive  second  chromosomes  from  their  father  which 
will  be  identical  with  those  present  in  the  Pi  not-speck  race  (in  the 
diagram  the  Dicha^t  race),  while  the  speck-Dichset  back-cross 
individuals  will  receive  the  second  chromosome  that  came  from  the 
other  Pi  race.  Since  the  two  types  are  alike  in  their  third  chromosome 
constitution,  and  since  they  have  been  reared  in  the  same  culture  bot- 
tles, so  that  environmental  influences  were  the  same,  any  differences 

1  With  the  exception  of  culture  1737  (see  Appendix),  all  were  from  10  or  more  successive  brother- 
sister  matings.  All  these  specks  were  from  the  same  Fs  pair.  All  those  before  culture  2430  were 
from  the  same  Fs  pair.  All  those  after  2430  were  from  a  different  Fs  pair,  but  were  themselves 
from  the  same  Fn  pair.     Fu  and  Fie  were  mass  cultures  instead  of  pairs. 


AN   ANALYSIS   OF   THE   EFFECT   OF   SELECTION 


25 


between  them  must  be  due  to  second-chromosome  differences  between 
the  two  Pi  races.  This  experiment  may  be  continued  further  by 
mating  the  not-speck  Dichaet  males  produced  by  the  back-cross  bo  the 
speck  not-Dichset  females.     Such  a  mating  should  gh  e  the  Bame  resuH 


n 


D' 


? 


n  n 


~v 


n  m 

_    d: 


Test 


I 


m 


B.C. 


n  i 

D' 


J*    DL 


n 


Fig.  13. 

as  the  first  back-cross  and  does  in  fact  do  so.  In  table  19  both  types  of 
experiment  are  treated  together.  Figure  14  is  a  graphical  representa- 
tion of  the  result  of  one  experiment  of  the  type  here  described. 

It  should  be  noted  that  such  experiments  are  suited  only  for  the 
detection  of  dominant  modifiers  present  in  one  Pi  race,  or,  stated 
conversely,  recessives  present  both  in  one  Pi  race  and  in  the  speck  race 
from  which  the  test  female  came. 


Table  19. — d1  Tests,  Chromosome  II. 


Source. 

Tested 
against — 

Means. 

Distributions. 

Not-sp. 

sp. 

Not-sp. 

sp. 

Diff. 

Diff. 
P.  E. 

X* 

69.4 
13.3 

•I  77 
17   7 

6  17 
19.0 

3  05 

P 

864 

sp.  stock 
sp.  stock 
sp.  stock 

1331 

1331 
sp.  stock 
sp.  stock 
sp.  stock 
sp.  stock 

sp.  stock 
sp.  stock 

1331 

1331 
sp.  stock 
sp.  stock 
sp.  stock 
sp.  stock 

1331 

5.314*0.045 
5.924*    .026 
5.824*    .062 
4.983*    .063 
6.095*    .043 
5.412*    .063 
4.711*    .062 
5.304*    .087 
4.353*    .067 

4.462*0.050 
5.732*    .031 
5.385*    .117 
4.438*    .065 
5.750*    .104 
4.686*    .097 
4.442*    .070 
4.762*    .101 
4.151*    .045 

+0.852*0.067 
+    .192*    .040 
4-    .439*    .132 
+    .545*    .091 
+    .345*    .113 
+    .720*    .116 
+    .268*    .093 
+   .542*    .133 
+   .202*     081 

12  7 
4.8 
3.3 

6.0 
3.  1 
6 . 3 
2.9 

■I    1 

0    (MMMHKJ- 

.004 
.10 
00] 
.05 
.0003 

.04 
M 

1002 

1002 

1002 

1002 

Cross-br.  plus.  . 
900 

Cross-br.  minus. 
Cross-br.  minus. 

Table  19  gives  the  results  of  the  experiments  of  this  type  thai  have 
been  carried  out.  (For  the  raw  data  see  Appendix.)  The  first  two 
columns  give  the  Pi  races,  or  in  cases  where  the  tested  male  came 
himself  from  a  back-cross  test,  the  original  source  of  his  not-speck 
and  speck  chromosomes.  The  third  column  gives  the  BOUTCe  of  the 
test  female.  All  tests  in  which  the  data  for  these  three  columns  were 
identical  have  been  lumped.     The  next  three  columns  give  the  mean 


26 


AN   ANALYSIS    OF   THE    EFFECT    OF    SELECTION. 


60 


50 


40 


30 


20 


10 


bristle  number  of  the  two  classes  of  Dichset  offspring  and  the  differ- 
ence between  these  two  means.  The  sign  of  the  difference  is  given  as 
positive  when  the  not-specks  had  a  higher  mean  than  the  specks  (as 
in  all  these  cases);  negative,  as  in  other  results  (see  below),  when 
the  specks  were  higher.     In  the  col- 

umn  headed  p^r  is  given  the  quotient 

of  the  difference  between  the  two  means 

divided  by  its  own  probable  error,  a 

measure  of  the  probable  significance  of 

that  difference.     The  last  two  columns 

give  the  x2  and  P  values  for  the  two 

(speck    and   not  speck)  distributions, 

considered  as  wholes. 
These  data  make  it  certain  that  the 

864  plus  line  and  crossbred  plus  line 

both    contained   second   chromosomes 

with  one  or  more  plus  modifiers  domi- 
nant to  minus  modifiers  in  the  second 

chromosome  of  the  speck  stock.     The 

1002  plus  line  had  similar  modifiers, 

and  also  had  the  same  relation  to  the 

1331  minus  line.     It  is  probable,  from 

the  results  obtained  with  the  1002  line, 

that  the  speck  stock  and  the  1331  line 

had  some  minus  modifiers  in  common, 

but  that  the  second  chromosome  of  the 

1331    line  was   more   strongly  minus. 

Both  these  latter  results  would  have 

been  expected,  since  the  second  chro- 
mosome of  the  1331  line  came,  in  part 
at  least,  from  that  of  the  speck  stock, 

but  has  been  minus  selected,  while  the  speck  stock  has  not  been 
selected  at  all  for  bristle  number. 

The  experiments  just  discussed  show  that  the  second  chromosome 
contains  one  or  more  modifiers,  but  give  us  no  information  regarding 
the  loci  of  such  modifiers.  It  is  possible,  on  the  basis  of  this  data 
alone,  that  speck  itself  is  the  minus  modifier.  If,  however,  a  heterozy- 
gous female  is  tested  by  mating  to  a  speck  not-Dichaet  male,  there 
will  be  a  possibility  of  crossing  over  between  speck  and  any  modifiers 
in  the  second  chromosome.  The  result  would  be  that  the  speck  and 
not-speck  offspring  differ  less  than  when  an  Fi  male  is  tested.  There 
is,  of  course,  also  an  opportunity  for  crossing  over  in  the  third  chromo- 
somes of  such  females,  so  that  the  Dichset  offspring  will  not  be  all 
alike  with  respect  to  their  third  chromosomes,  as  they  were  when  the 
male  was  tested;  but  the  same  crossover  classes  should  occur  among 


Fig.  14. — Not-speck  (solid  line)  and 
speck  (broken  line)  offspring  from 
male  back-cross  tests  of  864  inbred 
plus  line  against  speck  stock.  Curves, 
based  on  153  not-speck  and  106  speck 
flies,  are  both  reduced  to  the  percent- 
age basis.  See  table  19  for  statistical 
treatment. 


AN   ANALYSIS   OF   THE   EFFECT   OF   SELECTION. 


27 


both  the  speck  and  the  not-speck  offspring,  and  in  identical  propor- 
tions.    Therefore  this  factor  should  not  influence  the  end-result. 

Table  20  shows  the  results  obtained  from  such  experiment  The 
arrangement  is  the  same  as  in  table  19. 

As  was  expected,  the  differences  here  are  less  than  in  the  correspond- 
ing tests,  but  are  still  present  and  in  the  same  direction  when  significant . 
This  result  proves  that  one  or  more  of  the  second-chromosome  modi- 
fiers cross  over  from  speck  in  the  female. 


Table  20. —  9  Tests,  Chromosome  II. 


Source. 

Tested 
against — 

Means. 

Distributions. 

Not-sp. 

sp. 

Not-sp. 

sp. 

Diff. 

Diff. 
P.  E. 

X? 

P 

864 

864 

sp.  stock 
1331 
1331 

sp.  stock 
sp.  stock 

1331 

1331 
sp.  stock 
sp.  stock 

1331 

sp.  stock 

1331 
sp.  stock 

1331 

1331 
sp.  stock 

1331 
sp.  stock 

4.971±0.097 
4.674=*=    .059 
4.448=*=    .043 
5.543=*=    .074 
4.875±    .062 
4.617=*=    .046 
5.336=*=    .027 
5.259=*=    .097 
4.350=*=    .086 

4. 600=*=  0.082 
4.321=*=    .067 
4.245=*=    .044 
5.393=*=    .104 
4.787=*=    .070 
4.250=*=    .056 
5.390=*=    .048 
4.727=*=    .152 
4.609=*=    .090 

+0.371  ±0.127 
+   .353=*=    .089 
+    .203=*=    .062 
+    .150=*=    .128 
+    .088=*=    .093 
+    .367=*=    .073 

-  .054=*=    .055 
+    .532=*=    .180 

-  .259=*=    .125 

2.9 
4.0 
3.3 
1.2 
0.9 
5.0 
1.0 
3.0 
2.1 

4.59 
9.10 
13.1 
2  78 

1.39 
13.8 
8.93 

7 .  97 
2.21 

0.21 
.06 
004 

.43 
.92 
.03 
.26 
.05 
.34 

864 

1002 

1002 

1002 

1002 

Cross-br.  minus. 
Cross-br.  minus . 

THIRD-CHROMOSOME  MODIFIER. 

If  we  cross  two  races,  one  of  which  is  Dichset  rough,  the  other  wild- 
type,  the  Fi  female  will  have  the  constitution  D'  r0.  If  such  a  female 
be  mated  to  a  not-Dichffit  rough  male,  there  will  be  two  types  of 
Dichset  offspring— the  non-crossovers  will  be  rough,  the  crossovers 
not  rough.1  If  the  two  original  chromosomes  differed  in  modifying 
factors  somewhere  near  rough,  these  two  types  of  offspring  will  differ 
in  their  bristle  number. 

Such  tests  have  been  carried  out,  with  the  results  shown  in  table 
21. 2  In  only  one  case  (the  third)  was  a  significant  difference  obtained; 
but  that  case  proves  that  there  was  a  dominant  plus  modifier  in  the 
1002  line,  located  somewhere  near  rough,  or  a  dominant  minus  modifier 
in  the  speck  stock,  but  not  in  the  1331  line  and  in  the  same  region. 
Since  the  1331  line  was  derived  from  a  cross  involving  the  speck  Btock, 
and  had  been  minus  selected  ever  since  that  cross,  it  is  probable  that 
dominant  minus  modifiers  present  in  the  speck  stock  would  have  been 
preserved  in  the  1331  line.     It  is,  therefore,  almost  certain  that  the 

'There  will  be  some  double  crossovers,  but  these  will  be  rare.  There  will,  be  0OUTM,  also  be 
two  classes  of  not-Dichsets. 

2  In  the  case  recorded  in  the  second  row,  the  Dichyet  and  rough  ra.no  from  different  parent*, 
so  that  the  non-crossover  and  crossover  classes  are  reversed.  The  experiment  is  the  HUM  id 
principle  as  that  outlined  above. 


28 


AN   ANALYSIS    OF   THE    EFFECT    OF    SELECTION. 


1002  line  contained  a  dominant  plus  modifier  in  the  region  of  the 
rough  locus.1 

There  can  be  no  question  that  the  lines  studied  do  differ  in  their 
constitution  with  respect  to  definite  modifying  genes  that  affect 
bristle  number.  In  the  case  of  the  1002  and  1331  lines  there  is  at 
least  one  modifier,  and  probably  two,  located  in  different  chromosomes. 
This  gives  the  explanation  of  the  increased  variability  observed  in  F2 
when  these  lines  were  crossed.  The  only  other  available  explanation  of 
that  phenomenon — contamination  of  allelomorphs — has  already  been 
shown  above  to  lead  to  complications  in  this  case.  (See  also  below.) 
Since  it  is  both  improbable  and  unnecessary,  it  may  safely  be  dis- 
carded. 

Table  21. —  9  Tests,  Chromosome  III. 


Source. 

Tested 
against — 

Means. 

Distributions. 

Not-ro. 

ro. 

Not-ro. 

ro. 

Diff. 

Diff. 
P.  E. 

X2 

P 

Sp.  stock. 
1002 

Sp.  stock. 
Sp.  stock. 

864 
1331 
1002 
cross-br.  minus 

1331 
1331 
1331 
1331 

4.793±0.106 
4.750±    .071 
4.697±    .065 
4.323±    .089 

4.761±0.081 
4.581±    .091 
5.098±    .042 
4.276±    .092 

-0.032±0.133 
+    .169±    .115 
+    .401±    .077 
-    .047±    .127 

0.2 
1.5 

5.2 
0.4 

1.76 
1.09 
18.7 
0.33 

0.60 
.58 
.002 
.999 

THIRD-CHROMOSOME  LETHALS. 

Culture  1264,  belonging  to  the  third  generation  of  the  1002  inbred 
plus  line,  produced,  in  the  last  6  days  it  was  counted,  60  Dichsets  and 
no  not-Dichsets.  It  seemed  possible  that  one  of  the  parents  was 
homozygous  for  Dichset,  so  the  line  was  continued.  It  was  finally 
bred  through  about  18  generations,  and  produced  2,735  Dichsets  and 
only  4  not-Dichsets.  The  4  not-Dichsets  suggest  the  hypothesis  that 
all  the  Dichsets  are  really  heterozygous  as  usual,  but  that  they  carry 
a  lethal  in  the  other  chromosome  that  kills  the  not-Dichsets.2  That 
they  are  heterozygous  has  been  shown  by  out-crossing  them.  When 
mated  to  Dichsets  of  other  strains  the  result  was  211  Dichsets  to  103 
not-Dichsets  (4  cultures),  the  2  : 1  ratio  usually  obtained  when  Dichsets 
are  mated  together.  When  mated  to  not-Dichsets  the  result  was  207 
Dichsets  to  209  not-Dichsets  (6  cultures) — a  normal  1 :  1  ratio.  That 
there  is  a  lethal  in  the  stock  has  been  shown  by  mating  Dichsets  of 
this  strain  to  Extended  flies  and  inbreeding  the  not-Dichset  offspring, 
which  were  found  to  carry  a  lethal  as  expected.     (See  below.) 

1  The  second  row  of  table  18  seems  to  contradict  the  conclusion  that  the  1002  and  1331  lines 
differed  with  respect  to  a  modifier  near  rough.  However,  the  experiment  represents  only  a  few 
flies,  and  did  not  give  a  significant  result.  Moreover,  it  was  carried  out  before  the  1002  line 
had  been  very  long  inbred  (F&),  and  involved  a  not-rough  chromosome  from  that  line,  which  had 
not  then  become  homozygous  for  rough. 

2  See  Muller  (1917)  for  a  discussion  of  autosomal  lethals. 


AN    ANALYSIS   OF   THE    EFFECT    OF    BBLECTION. 


29 


The  4  not-Dichaet  flies  produced  by  uncrossed  descendants  of  1204 
appeared  in  cultures  1516,  2424,  2571,  and  2851.  Since  most  of  the 
flies  of  this  line  are  heterozygous  for  other  factors  in  Chromosome  III. 
it  should  be  possible  by  an  examination  of  these  4  flies  to  determine  on 
which  side  of  Dichset  the  lethal  lies;  for  these  flies  are  evidently  en 
overs  between  Dichset  and  the  lethal,  and  should  show  certain  relar 
tions  with  the  other  characters,  depending  on  the  locus  of  the  factor. 

The  4  cultures  in  question  gave  the  results  shown  in  table  22    both 
parents  in  1264  being  rough,  all  these  flies  are  rough). 

Table  22. 


1516 
2424 
2571 

2851 


D'. 


D'  ss  so. 


D'so. 


106  6  4  10 

78  Dichsets,  some  ss.  0  1 

49  Dichsets,  with  some  D'  pe  ss  so.  0  0 

41  Dichsets,  1  not  D';  other  characters  not  noted. 


not-D'. 


not-D'  ss. 


not-D'  so. 


0 

1 


Since  the  other  characters  were  not  noted  in  2851,  that  bottle  is 
useless  for  our  present  purposes.  The  constitution  of  the  parents  in 
the  other  three  cultures  must  have  been  as  follows: 


D' 


D' 


1516: 

kuSs 

es 

l\uss  es 

2424: 

D' 

kllSs 

D' 

huSs 

2571: 

D' 

knpp 

ss 

e' 

lpv  ss  e* 

Since  there  can  be  no  crossing  over  in  the  male,  there  must  in  each 
case  have  been  a  crossover  between  D'  and  lm  in  the  female.  1516 
indicates  that  lm  is  to  the  right  of  D'\  2424,  to  the  left  if  the  individual 
was  a  single  crossover.  But  the  distance  D'  s„  here  involved,  is 
known  to  be  long  enough  so  that  double  crossovers  sometimes  occur 
in  it.  In  2571  the  distance  involved  is  D'  pp,  which  is  too  short  for 
a  double  crossover,  therefore  llu  is  to  the  right  of  D'.  The  position 
of  lul  being  thus  obtained,  the  not-D'  produced  by  2424  must  hi 
been  a  double  crossover. 

The  next  problem  is:     How  far  from  Dichset  is  the  lethal  locus'.' 
The  mating  is  always — 

J^-'x  — 

lm       hu 

There  being  no  crossing  over  in  the  male,  the  sperm  are  of  two 
kinds  only— D'  and  lm.     The  non-crossover  eggs  are  of  the  same 


30 


AN   ANALYSIS   OF   THE   EFFECT   OF   SELECTION. 


constitution,  but  there  are  also  the  crossover  eggs,  D'  /„„  and  +. 
If  we  let  the  non-crossovers  be  to  the  crossovers  as  x :  y,  the  result  of 
the  mating  will  be: 


D' 

D 

iy 

hu 
hu 
D' 

-n —  =  dies 
tin 


7  =  dies. 
=  D'. 
=  D'. 


y 


Wm 


D' 
D'lm 


=  dies. 


hu 


=  dies. 


+ 


r=-=not-D'. 
tin 


The  result  then  is: 


Per  cent  crossovers  = 


2x-\-y  =  T>'  y  =  not-T>' 

WOy     200  (not-D') 


x+y     D'+not-D' 


In  the  present  case  this  formula  gives  the  crossover  percentage 
as  0.29.     Lethal  III  is,  then,  located  0.29  to  the  right  of  Dichset. 

Another  lethal  of  the  same  sort  as  the  one  just  described  appeared 
in  culture  1546.  This  culture  belonged  to  the  sixth  generation  of  the 
same  line  in  which  the  first  lethal  was  found,  and  was  descended  from 
a  sister  pair  (1213)  to  1264,  the  first  culture  in  which  that  lethal  ap- 
peared. Since  the  two  lethals  are  certainly  distinct,  as  will  appear 
below,  this  relationship  is  to  be  regarded  only  as  a  coincidence.  Three 
cultures  of  this  strain  were  made — 1546  and  two  daughter  pairs. 
The  result  was  154  Dichsets  and  1  not-Dichset.  The  1  not-Dichset 
was  from  culture  1681.  The  Dichsets  from  this  culture  show  both 
parents  to  have  had  the  constitution 

_zy 

Sgl      SgCgTo 

The  not-Dichset  individual  was  spineless,  sooty,  rough.  This  indi- 
cates that  the  lethal  was  to  the  left  of  Dichaet;  otherwise  the  egg  in 
question  must  have  resulted  from  a  sepia  Dichset  spineless  triple  cross- 
over, which  is  a  very  rare  occurrence.  By  the  method  outlined  above 
it  may  be  calculated  that  the  lethal  gives  1.29  per  cent  of  crossovers 
with  Dichset. 

That  these  two  lethals  are  distinct  is  indicated  by  the  following 
culture,  1915.  The  female  of  this  mating  came  from  culture  1791, 
which  gave  31  Dichsets  and  no  not-Dichsets.  1791  was  an  F2  from  a 
cross  involving  1419  of  the  1264  line,  and  thus  its  lethal  must  be  sup- 
posed to  be  that  of  1264.  The  male  of  the  test  bottle  1915  was  from 
1681  of  the  second  lethal  strain.  Therefore,  if  the  two  lethals  are  the 
same,  1915  should  have  given  few  or  no  not-Dichsets;  if  they  are  dif- 
ferent it  should  have  given  2  Dichsets  to  1  not-Dichset.     The  actual 


AN   ANALYSIS   OF   THE   EFFECT   OF   SELECTION.  .'^1 

result  was  51  Dichaets  to  30  not-Dichaets.  Evidently,  then,  the  two 
lethals  are  distinct,  as  was  previously  indicated  by  the  fact  that  they 
are  probably  on  different  sides  of  Dichaet. 

It  seemed  possible  at  first  that  one  or  both  of  these  lethals  might 
be  due  to  a  breaking  up  of  the  Dichaet  factor,  whereby  its  lethal  effect 
had  been  separated  from  the  effect  it  produces  on  the  soma  of  b  ! 
erozygous  fly.  This  hypothesis  is  negatived  by  two  considerations: 
(1)  both  lethals  have  been  shown  to  occupy  loci  different  from  that 
for  Dichaet;  (2)  the  lethal  effect  of  Dichaet  is  not  allelomorph ic  to  that 
of  these  factors,  since  a  fly  with  Dichaet  in  one  chromosome  and  either 
of  the  lethals  in  its  mate  does  not  die. 

EXTENDED. 

In  culture  1379,  of  the  crossbred  plus  series,  there  appeared  several 
flies  intermediate  in  appearance  between  Dichaet  and  the  normal. 
These  flies  had  the  bristles  of  the  normal  flies  (including  the  anterior 
post-alars,  always  reduced  or  absent  in  Dichaets),  but  had  their 
wings  spread  out  to  a  greater  or  less  extent.  These  individuals  were 
tested,  and  were  found  to  have  a  dominant  factor,  responsible  for  the 
extended  wing  character.  The  character  has  been  called  " Extended" 
(see  plate  1,  fig.  1).  It  occasionally  overlaps  the  normal,  and  is  there- 
fore not  favorable  for  linkage  experiments.  It  is,  however,  sufficiently 
uniform  in  appearance  to  make  it  possible  to  work  out  its  inheritance 
with  certainty.  The  gene  is  found  to  be  an  allelomorph  of  Dichaet, 
and  is  designated  De.  Like  Dichaet,  it  is  lethal  when  homozygous; 
and  the  flies  with  Dichaet  in  one  chromosome  and  Extended  in  the 
other  also  die.     These  conclusions  are  based  on  the  following  results: 

Preliminary  experiments  involving  speck  (chromosome  II)  and 
various  characters  in  chromosome  III  showed  that  Extended  crosses 
over  freely  from  speck  in  the  male,  but  gives  apparently  no  crossing 
over  in  the  male  with  sepia,  spineless,  or  rough.  These  data  arc  not 
very  satisfactory,  owing  to  the  fact  that  some  of  the  Extended  flies 
are  very  similar  in  appearance  to  the  not-Extended,  and  there  is  too 
great  an  opportunity  for  being  influenced  by  the  other  characters  of 
the  flies  when  making  the  separation.  However,  no  crossovers  were 
discovered  among  308  flies. 

When  tests  were  made  of  heterozygous  females,  there  was  found 

to  be  a  slight  excess  of  not-Extended  offspring,  presumably   due  to 

incorrect  classification.     The  proportion  of  crossovers,  based  on  Ex- 

13 
tended  offspring  only,  was  7^=12.4  per  cent  for  sepia  Extended 

11  Wb 

and  777  =  7.6  per  cent  for  Extended  spineless.     In  one  experiment  in 

which  all  three  of  these  factors  were  observed  at  once,  the  result  shown 
in  table  23  was  obtained. 


32 


AN    ANALYSIS    OF   THE    EFFECT    OF    SELECTION. 


It  is  evident  from  these  data  that  Extended  is  between  sepia  and 
spineless,  some  distance  from  either.  It  is,  then,  in  the  same  general 
region  as  Dichaet. 

The  lethal  effect  of  Extended  has  been  tested  in  two  ways.  Mat- 
ings  of  Extended  by  Extended  gave  116  Extended  to  94  normals. 
If  homozygous  Extended  is  viable  the  result  should  be  3  :  1 ;  if  it 
dies  the  result  should  be  2  :  1.  In  fact,  it  was  nearer  1:1.  This 
result  is  probably  due  to  the  overlapping  phenomenon,  resulting  in  the 
classification  of  some  Extended  flies  as  normal.  It  is  suggestive  of  a 
2  : 1  ratio,  however.  More  conclusive  data  was  obtained  by  mating 
heterozygous  Extended  to  Dichset  flies  heterozygous  for  lethal  III 
(see  above),  and  inbreeding  the  Extended  offspring.  If  Extended  is 
lethal  when  homozygous,  these  flies  should  produce  only  Extended 
offspring,  but  these  should  all  be  heterozygous.  They  should,  in  fact, 
breed  exactly  like  the  true-breeding  race  of  Dichaets  described  above. 
This  is  actually  the  case.  Such  a  stock  has  now  been  kept  for  four 
months,  and  is  still  made  up  almost  entirely  of  evidently  Extended  flies; 
but  tests  show  them  to  be  only  heterozygous  for  the  character. 


Table  23. 

De 

D< 

&e  ss 

Ss 

ssDe 

Dess 

se 

N 
0 

se  De  ss 

Total. 

39 

37 

3 

3 

6 

10 

1 

99 

The  mating  of  Dichaet  X  Extended  (or  vice  versa)  gave  the  following 
result:  Dichset,  99;  Extended,  69;  normal,  102;  total,  270.  If  we 
suppose  some  of  the  flies  classified  as  " normal"  to  be  in  reality  Ex- 
tended, this  result  approximates  to  the  1:1:1  expected  if  Dichaet- 
Extended  flies  die.  The  fact  that  the  Dichaets  are  only  about  a  third 
of  the  total  shows  that  half  the  Dichaet  gametes  have  been  eliminated 
somehow.  One  of  the  Dichaets  and  a  number  (4  individual  matings 
and  2  mass  cultures)  of  the  Extendeds  have  been  tested,  and  neither 
sort  has  produced  the  other.  It  is,  then,  safe  to  conclude  that  Dichaet- 
Extended  flies  die. 

Culture  1379,  in  which  Extended  first  appeared,  was  made  up  by 
mating  together  two  8-bristled  flies,  the  male  from  1145,  the  female 
from  1253.  The  latter  culture  gave  among  other  offspring  5  sevens 
and  2  eights.  The  other  eight,  in  1356,  behaved  normally,  as  did 
one  of  the  sevens  (in  1357).  Culture  1145,  however,  gave  no  seven 
and  only  the  single  eight.  Since  1379  gave  a  result  indicating  that  one 
parent  was  Extended  instead  of  8-bristled  Dichaet,  it  seems  probable 
that  the  male  parent,  from  1145,  was  the  mutant.  In  either  case, 
the  Extended  parent  was  produced  by  mating  a  7-bristled  Dichaet 


AN   ANALYSIS   OF   THE   EFFECT   OF   SELECTION.  33 

female  to  a  6-bristled  Dichset  male,  both  parents  being  from  the  cr« 
bred  plus  selection  series. 

It  follows  from  the  data  presented  above  that  Extended  is  an  allelo- 
morph of  Dichset  intermediate  between  Dichset  and  its  normal  allelo- 
morph in  its  somatic  effect,  and  that  it  arose  in  a  fly  heterozygous  for 
these  two  factors.  It  is,  then,  the  kind  of  thing  one  would  expect 
contamination  of  allelomorphs  to  produce.  On  the  other  hand,  it 
seems  at  least  equally  possible  to  suppose  that  it  arose  as  a  mutation 
of  one  or  the  other  allelomorph,  without  the  presence  of  the  other  or 
the  one  having  had  any  influence  on  the  event.  In  any  case,  the 
process  must  be  an  extremely  rare  one,  for  it  has  been  detected  only 
once,  in  spite  of  the  very  large  number  of  offspring  of  heterozygous 
Dichset  flies  that  have  been  observed  and  bred. 

Since  the  Extended  flies  have  more  bristles  than  Dichsets,  it  may  be 
supposed  that  the  fact  that  the  former  arose  in  a  plus-selected  series 
is  significant.  Such  a  supposition  has  actually  been  made  by  Castle 
(Castle  and  Phillips,  1914,  etc.)  with  regard  to  a  similar  case  in  hooded 
rats.  As  has  been  pointed  out  by  MacDowell  (1916),  a  mutation  in 
the  direction  in  which  selection  is  being  made  has  a  very  much  better 
chance  of  being  discovered  than  has  one  in  the  opposite  direction. 
Moreover,  these  mutations  have  been  demonstrated  only  in  an  ex- 
tremely small  number  of  cases;  and  a  very  elementary  knowledge  of 
the  theory  of  probability  will  suffice  to  convince  one  that  a  considerable 
number  of  cases  must  be  established  before  one  can  conclude  that  muta- 
tions are  more  likely  to  occur  in  one  direction  than  in  another.  No 
argument  based  on  one  or  two  cases,  however  well  established  those 
cases  may  be,  can  carry  any  conviction. 

"DICH/ETE  INTERMEDIATE." 

The  Star  Dichset  stock  in  the  Columbia  laboratory  was  found  to 
have  in  it  some  flies  that  were  indistinguishable  from  Extended.  It 
seemed  possible  that  these  flies  were  due  to  an  independent  occurrence 
of  the  Extended  mutation.  Since  the  Star  Dichset  stock  is  kept  by 
mating  (Star)  Dichset  flies  together  in  each  generation,  the  mutation 
responsible  for  these  " intermediates"  must  either  have  occurred  in  a 
Dichset  fly  (as  did  the  Extended  mutation),  or  have  been  in  the  stock 
since  it  was  made  up.  The  fact  that  Dichsets  are  mated  together  in 
continuing  the  stock  seemed,  however,  to  show  that  the  character 
was  not  true  Extended,  since,  as  we  have  seen  above,  Dichffit-Extended 
flies  always  die.  But  the  possibility  remained  that  "  intermedial  e"  was 
another  non-lethal  allelomorph  of  Dichset.  Accordingly,  tests  were 
made  as  follows : 

Matings  of  Dichset  by  Dichset  gave  some  intermediates,  showing 
that  the  continuance  of  the  character  in  the  stock  was  not  dependent 
on  the  use  of  non-virgin  females,  and  proving  that  the  character  was 
not  Extended. 


34  AN   ANALYSIS    OF   THE    EFFECT    OF    SELECTION. 

Matings  of  intermediates  by  intermediates  gave  both  intermediates 
and  normals,  showing  that  the  character  was  either  dominant  or  irreg- 
ular in  appearance. 

Matings  of  intermediate  to  specks  and  to  black  purples  of  other 
stocks  gave  only  normals,  showing  the  character  to  be  recessive. 

Mating  together  the  Fi  normals  from  the  last  type  of  matings  gave 
a  few  intermediates;  but  these  were  in  no  case  speck  or  black  or  purple. 
This  is  the  usual  behavior  of  a  second-chromosome  recessive,  due  to 
no  crossing  over  in  the  Fi  male.  Hence  " intermediate"  is  a  recessive 
character,  and  lying  in  the  second  chromosome.  Its  occurrence  in 
the  Star  Dichaet  must  have  been  only  a  coincidence,  and  can  have  had 
nothing  to  do  with  the  presence  of  Dichaet  in  that  stock.  The  differ- 
ence between  this  character  and  Extended  is  a  striking  illustration 
of  the  danger  of  arguments  as  to  the  identity  of  characters  based  on 
similarity  of  appearance. 

NOT-DICH&TS  FROM  SELECTED  LINES. 

As  has  already  been  pointed  out,  Dichaet  flies  almost  always  have 
fewer  bristles  than  have  normals.  All  Dichaets  are  heterozygous  for 
the  normal  allelomorph.  Therefore,  in  such  an  experiment  as  this 
one,  in  which  Dichaets  are  repeatedly  mated  together,  one  obtains 
normal  flies  the  not-Dichaet  genes  in  which  have  been  associated  with 
Dichaet  genes  for  many  generations.  The  experiment  is,  then,  suited 
for  a  study  of  the  question  as  to  whether  or  not  factors  " contaminate" 
their  allelomorphs.  If  this  contamination  occurs,  one  might  expect 
the  not-Dichset  flies  to  show  a  tendency  to  have  fewer  bristles  than 
they  normally  have,  and  the  Dichaets  to  have  more.  That  Dichaets 
tend  to  increase  in  bristle  number  is  very  improbable.  The  stock 
has  now  been  kept,  always  of  necessity  in  heterozygous  condition,  for 
more  than  40  generations.  There  is  no  evidence  that  any  progressive 
change  has  occurred,  though  no  selection  has  been  used  in  keeping 
the  stock  cultures.  The  modal  class  at  present  (5  bristles)  is  actually 
lower  than  the  class  (6)  of  the  original  mutant.1 

There  are  some  data  regarding  the  bristles  of  the  not-Dichaets  pro- 
duced bv  selected  Dichaets.  Counts  of  these  bristles  have  been  taken 
only  occasionally  (see  table  24),  but  whenever  a  bristle  number  other 
than  8  has  been  observed  in  such  flies  it  has  been  noted  on  the  record 
sheet.  Examination  of  these  notes  shows  that  in  the  minus-selected 
series  there  are  several  records  of  6  and  7  bristled  not-Dichaets,  but 
none  of  numbers  higher  than  8.  In  the  plus  selected  lines  there  are  a 
number  of  records  of  nines  and  tens,  but  no  sixes  and  only  1  seven 
(from  1190,  an  F6  of  the  crossbred  plus  series).  The  complete  counts 
taken  of  bristle  numbers  are  given  in  table  24. 

JIt  may  be  pointed  out  that  the  familiar  yellow  mouse  and  several  similar  cases  in  Drosophila 
afford  evidence  of  the  same  sort  against  contamination. 


AN   ANALYSIS    OF   THE    EFFECT   OF    SELECTION. 


There  is  no  evidence  for  contamination.  With  the  one  exception 
noted  above,  all  the  variations  are  in  the  direction  for  which  the 
Dichsets  were  being  selected.  On  the  multiple-factor  view  one  would 
expect  this  result,  since  it  would  seem  likely  that  any  modifier  would 
usually  affect  Dichsets  and  not-Dichsets  in  the  same  direction.  The 
one  exception,  a  7  from  1190  of  the  crossbred  plus  series,  is  Bcarcely 
surprising  on  this  hypothesis,  in  view  of  the  facts  that  unselected  not- 
Dichset  races  may  produce  sevens  (see  table  2),  and  that  1190  was  pr<  >b- 
ably  not  homozygous  for  a  large  number  of  plus  modifiers.  Since 
this  individual  was  not  tested,  it  would  perhaps  be  futile  to  argue  the 
case  further. 

Table  24. 


Culture. 

Series. 

Genera- 
tion. 

Bristle  Nos. 

6 

7 

8 

9 

10 

1277 
1285 
1357 
1810 
1811 
1268 
1273 
1878 
1879 
1881 
1882 
1892 
1986 
1996 
2015 

864  plus 

7 

7 

8 

10 

7 

6 

7 

10 

10 

10 

10 

10 

5 

5 

11 

1 

57 
35 
33 
51 
16 
13 
33 
15 
20 
23 
31 
10 
12 
34 
88 

Crossbred  plus 

Crossbred  plus 

864  plus 

1002  plus 

1 

1 
4 

Crossbred  minus. . .  . 
Crossbred  minus. . .  . 
Crossbred  minus .... 

Crossbred  minus. . . . 
Crossbred  minus. . .  . 
Crossbred  minus. . .  . 
1331  (speck)  minus. 
1331  (speck)  minus. 
Crossbred  minus. . . . 

It  may  be  noted  here  that  in  the  Star  Dichset  stock  referred  to  above 
(p.  31)  there  wrere  found  to  be  numerous  not-Dichsets  with  9  and  10 
bristles.  Unfortunately,  no  counts  were  made  on  these  flies,  and  the 
nature  of  the  extra  bristles  was  not  determined.  The  stock  h:is  since 
been  "purified,"  to  rid  it  of  certain  other  mutations,  and  the  extra- 
bristled  flies,  formerly  plentiful,  have  now  disappeared.  This  stuck, 
as  stated  above,  was  continued  by  mating  together  (Star)  Dichset 
flies,  without  regard  to  bristle  number.  These  extra-bristled  not- 
Dichsets  therefore  furnish  evidence  of  the  same  type  as  thai  just  dis- 
cussed, except  that  the  race  was  not  selected  for  bristle  number. 


36  AN   ANALYSIS   OF  THE   EFFECT   OF   SELECTION. 

GENERAL  DISCUSSION. 

THE  SELECTION  PROBLEM :  QUESTIONS  AT  ISSUE. 

It  appears  to  the  writer  that  the  three  questions  below  are  the  chief 
ones  at  issue  in  the  discussion  of  the  selection  problem: 

1.  Does  selection  use  germinal  differences  already  present,  or  differences 

that  arise  during  the  experiment,  or  both? 

2.  In  case  it  uses  new  differences,  does  it  cause  them  to  occur  more 

frequently,  and  does  it  influence  their  direction? 

3.  Are  differences,  already  present  or  arising  de  novo,  more  likely  to 

occur  in  the  locus  of  the  gene  under  observation,  or  in  other  loci? 

It  is  not,  I  think,  questioned  by  any  one  that  selection  may  effect 
either  gradual  or  sudden  change  in  the  mean  character  of  mixed  races, 
or  that  it  may  even,  occasionally,  produce  such  an  effect  in  pure  races 
if  a  mutation  in  the  desired  direction  happens  to  occur. 

1.  Does  selection  use  germinal  differences  that  are  already  present,  or  differences 
that  arise  during  the  experiment  ? 

Everyone  who  has  bred  animals  or  plants  is  familiar  with  the  fact 
that  different  strains,  even  when  rather  closely  related,  differ  in  all 
sorts  of  minor  points — size,  proportions  of  organs,  shade  of  color,  resist- 
ance to  disease,  fertility,  temperament,  rate  and  habit  of  growth — 
in  fact,  in  almost  any  respect  that  one  investigates.  This  can  only 
mean  that  such  strains  differ  genetically;  and  since  the  kinds  of  differ- 
ences are  usually  so  numerous,  they  probably  usually  have  many 
genetic  differences — i.  e.,  they  differ  in  respect  to  many  factors.  In 
any  race  not  normally  self-fertilizing  or  closely  inbred,  crosses  between 
individuals  of  different  constitution  must  then  be  frequent.  And 
such  crosses  must,  on  the  assumption  that  the  original  differences  were 
Mendelian,  lead  to  the  production  of  a  population  more  or  less  hetero- 
zygous for  factors  that  produce  minor  effects  on  all  sorts  of  charac- 
ters. The  assumption  that  the  differences  are  Mendelian  rests  on  the 
observed  facts,  (1)  that  demonstrably  Mendelian  factors  may  produce 
effects  on  practically  any  kind  of  character  studied,  and  effects  of 
practically  any  observable  degree ;  and  (2)  that  non-Mendelian  inher- 
itance has  never  been  demonstrated,  except  for  a  few  cases  of  plastic 
characters  in  plants  and  cases  of  infectious  diseases.1  Other  kinds 
of  inheritance  may  exist ;  but  the  available  data  indicate  that  they  must 
be  extremely  rare.  Therefore  the  chances  are  that  any  observed 
difference  between  two  strains  is  Mendelian. 

If  these  conclusions  be  accepted,  it  follows  that  any  strain  not  very 
closely  inbred  is  likely  to  be  heterozygous  for  factors  influencing  many 
characters.  Selection  for  these  characters  will  then  be  effective  in 
isolating  favorable  combinations  of  such  "modifying  factors." 

JOne  may  refuse  to  call  these  cases  of  inheritance  if  he  chooses  to  de6ne   that  term  so  as  to 
exclude  them. 


AN   ANALYSIS   OF   THE    EFFECT    OF    SELECTION.  :\~ 

Mendelian  differences  are  still  arising  by  mutation  and  may  arise 
in  a  selection  experiment  as  well  as  anywhere  else;  and  those  that  a 
in  such  an  experiment  are  as  likely  to  affect  the  character  under  ob- 
servation as  are  any  Mendelian  differences  taken  at  random.  J* 
therefore  probable  that  selection  sometimes  makes  use  of  variations 
that  arise  during  the  course  of  the  experiment,  or,  rather,  that  varia- 
tions which  may  be  available  do  arise. 

The  question  is,  what  is  the  relative  frequency  of  the  two  kinds  of 
available  factor  differences— those  already  present  and  those  that  arise 
de  novo?  The  answer  is  found  by  investigation  of  the  data  on  selection 
in  inbred  lines  and  in  crossbred  lines.  In  closely  inbred  strains  there  are 
not  likely  to  be  many  factor  differences  present  when  selection  is  begun, 
while  in  crossbred  lines  these  differences  are  likely  to  be  numerous. 

That  selection  is  usually  effective  in  crossbred  lines  is  a  well-known 
fact,  demonstrated  many  times  with  many  different  organisms.  Not 
many  experiments  have  been  carried  out  on  closely  inbred  material, 
but  those  of  Johannsen  (1903),  MacDowell  (1917),  and  the  present 
paper  (p.  11)  show  that  selection  may  be  without  effect  in  such  lines. 
In  two  of  these  cases  selection  was  effective  until  the  lines  became  highly 
inbred.  But  mutations  influencing  the  characters  under  observation 
have  been  obtained  in  the  selection  experiments  of  Castle  and  Phillips 
(1914),  Morgan  (Morgan,  Sturtevant,  Muller,  and  Bridges,  1915, 
p.  205),  Lutz  (1911),  and  those  reported  in  this  paper  (p.  31).1 

Apparently,  then,  selection  produces  its  effects  chiefly  through 
isolation  of  factors  already  present,  but  occasionally  available  muta- 
tions do  arise  during  the  course  of  the  experiment. 

2.  Does  selection  cause  mutations,  or  influence  their  direction? 

The  usual  selection  experiment  consists  in  breeding  from  individuals 
that  are  extreme  in  some  respect.  This  extreme  character  may  be 
environmental  in  origin,  or  it  may  be  caused  by  germinal  differences. 
In  the  first  case,  no  geneticist  is  likely  seriously  to  maintain  that  selec- 
tion will  have  any  effect  whatever.  In  case  the  extreme  character 
is  germinal  in  origin,  selection  will  of  course  be  effective  in  eliminating 
certain  genetic  types.  Moreover,  given  a  combination  of  genes  thai 
produce  the  character  in  a  certain  degree,  we  are  evidently  in  a  better 
position  to  reach  a  further  stage  than  if  we  have  the  character  less  well 
developed.  For  how  long  a  tail  will  be  when  it  gains  an  inch  evidently 
depends  on  how  long  it  was  before  it  gained  that  inch.  But  it  seems 
incomprehensible  that  selection  of  individuals  of  a  constitution  favor- 

'Evidence  derived  from  forms  that  reproduce  ascxually  is  also  available  in  studying  this 
question,  for  such  reproduction  commonly  prevents  recombination,  :in>l  therefore  gives  result* 
comparable  with  those  obtained  from  homozygous  strains.  Some  of  the  svidenoa  obtained  from 
studies  on  asexually  produced  Protozoa  (e.  g.,  Calkins  and  Gregory,  L913;  Jennings,  L910;  Middle- 
ton,  1915)  has  shown  that  selection  may  be  very  successful  in  whanging  such  forme.  But  it  ifl 
very  doubtful  if  these  animals  are  comparable  with  the  Metazoa  in  the  method  of  distribution 
of  their  chromatin.  It  seems  not  improbable  that  in  some  cases  recombination  nmy  hero  !>« 
possible  in  asexual  reproduction. 


38  AN   ANALYSIS    OF   THE    EFFECT    OF    SELECTION. 

able  to  the  development  of  a  given  character  can  make  more  likely 
the  occurrence  of  factorial  variations  affecting  that  character,  or 
variations  affecting  it  in  a  given  direction.  As  a  matter  of  fact,  there 
is  no  evidence  for  such  a  conclusion.  The  occurrence  of  mutations  is 
ordinarily  such  an  extremely  rare  phenomenon  that  it  would  be  very 
difficult  to  obtain  statistically  significant  data  in  the  matter.  More- 
over, when  one  is  selecting  for  a  character,  one  is  examining  his  animals 
or  plants  for  that,  character  with  unusual  care,  so  that  any  mutations 
in  that  character  are  very  likely  to  be  observed  and  tested,  provided 
they  are  in  the  direction  in  which  selection  is  being  carried  out.  It 
follows  from  these  considerations  that  extremely  careful  controls  are  re- 
quired before  any  data  on  these  questions  can  have  any  significance. 

3.  Are  variations  more  likely  to  occur  in  the  locus  of  the  gene  under  observation, 
or  in  other  loci? 

In  Drosophila  over  25  different  and  independent  mutant  factors  affect 
the  color  of  the  eye.  In  mice  there  are  7  or  more  independent  factors 
affecting  coat-color.  According  to  Little  (1915)  there  are  2  and  prob- 
ably 3  independently  segregating  factors  that  affect  spotting  in  these 
animals.  There  are  at  least  14  and  probably  more  definite  genes  (in 
different  loci)  that  affect  bristle  number  in  Drosophila,  not  counting 
the  "modifying  factors"  studied  by  MacDowell  and  the  writer. 

In  view  of  these  and  many  similar  facts,  it  is  certain  that  changes 
in  a  given  character  may  be  brought  about  by  changes  in  many  differ- 
ent parts  of  the  germ-plasm.  If  selection  of  a  given  mutant  race,  say 
hooded  rats  or  Dichset  Drosophila,  is  likely  to  cause  or  to  isolate  muta- 
tions in  the  gene  that  differentiates  that  race  from  the  normal  type 
(i.  e.,  the  hooded  factor  or  the  Dichset  factor)  rather  than  in  any  other 
factors,  it  follows  that  mutant  allelomorphs  must  be  more  variable 
than  " normal"  ones.  For,  by  analogy  with  mice,  hooded  rats  are 
homozygous  for  the  normal  allelomorphs  of  several  possible  factors 
affecting  spotting;  and  Dichset  flies  are  certainly  homozygous  for  the 
normal  allelomorphs  of  at  least  13  mutant  factors  that  affect  bristle 
number.  It  may  be  true  that  mutant  factors  are  on  the  average  more 
variable  than  their  normal  allelomorphs;  but  no  evidence  to  that 
effect  is  at  hand;  and  owing  to  the  great  difficulty  of  statistical  treat- 
ment of  the  frequency  of  mutations  alluded  to  above,  such  evidence 
will  be  very  difficult  to  obtain.1 

In  the  absence  of  such  evidence,  it  is  more  probable  that  variations 
will  appear  in  other  factors,  since  there  are  many  of  them  to  vary, 
but  commonly  only  one  that  is  responsible  for  the  difference  under 
observation.  That  changes  of  the  one  factor  itself  may  occur  in  selec- 
tion experiments,  however,  has  been  shown  by  Castle  (Castle  and 
Wright,  1916)  and  the  writer  (p.  31).  It  does  not  follow  that  selection 
has  caused  these  variations  or  that  they  are  more  likely  to  occur  than 
are  variations  in  other  factors. 

'Evidence  has   been   obtained  by  Emerson  (1917),  who  used  unusually  favorable  material, 
that  shows  clearly  that  different  allelomorphs  may  at  times  differ  greatly  in  their  mutability. 


AN   ANALYSIS   OF   THE    EFFECT    OF   SELECTION. 
CONTAMINATION  OF  ALLELOMORPHS. 

When  two  races  that  differ  in  quantitative  characters  are  crossed, 
it  is  frequently  observed  that  Fx  is  fairly  uniform,  and  thai  1',  Bhi 
an  increase  in  variability  together  with  the  production  of  forms  inter- 
mediate between  the  parent  races  and  often  different  from  the  \-\. 
There  are  two  current  methods  of  accounting  for  these  i 

(1)  The  two  races  are  assumed  to  have  differed  in  a  number  of 
Mendelian  factors  affecting  the  character  in  question.  The  observed 
result  is  then  explained  as  due  to  the  recombinations  of  those  factors. 

(2)  The  two  races  are  assumed  to  have  differed  in  only  one  factor 
affecting  the  character  in  question,  and  the  new  types  observed  id  i 
are  supposed  to  be  due  to  "contamination"  in  the  Fi  hybrid,  that  is, 
allelomorphs  present  in  the  heterozygote  are  supposed  to  have  influ- 
enced each  other,  so  that  they  do  not  come  out  unchanged. 

The  fundamental  principle  of  the  first  explanation — that  more 
than  one  factor  may  influence  the  same  character — is  admitted  by 
all  Mendelians.  But  many  of  the  adherents  of  that  explanation  are 
unwilling  to  admit  that  "contamination  of  allelomorphs"  has  ever 
been  experimentally  demonstrated.  Let  us  then  examine  the  evi- 
dence that  is  brought  forward  in  support  of  that  assumption. 

The  following  quotations  are  the  chief  ones  bearing  on  the  ques- 
tion that  I  have  been  able  to  find  in  recent  literature: 

"The  currently  accepted  explanation  (of  size  inheritance),  which  its 
supporters  choose  to  call  'Mendelian,'  rests  upon  the  idea  of  gametic  purity 
in  Mendelian  crosses.  It  assumes  that  Mendelian  unit-characters  are  un- 
changeable and  unvarying,  and  that  when  they  seem  to  vary  this  is  due  to  a 
modifying  action  of  other  unit-characters  (or  factors)  ....  The  idea 
of  unit-character  constancy  is  a  pure  assumption.  In  numerous  cases  unit- 
character  inconstancy  has  been  clearly  shown,  as  in  the  plumage  and  toe 
characters  of  poultry  according  to  the  observations  of  Bateson  and  Daven- 
port, and  the  coat-characters  and  toe-characters  of  guinea-pigs  in  my  own 
observations.  Unit-character  inconstancy  is  the  rule  rather  than  the  ex- 
ception."    (Castle,  19166,  p.  209.) 

"  .    .    .    .1   have   shown   in   numerous   specific   cases    that    when    unlike 
gametes  are  brought  together  in  a  zygote  they  mutually  influence  each  otl 
they  partially  blend,  so  that  after  separation  they  are  less  different  than  they 
were  before.     The  fact  remains  to  be  accounted  for  that  partial  blending  does 
occur  (1)  when  polydactyl  guinea-pigs  are  crossed  with  normals   (Castle, 
1906);  (2)  when  long-haired  guinea-pigs  are  crossed  with  short-haired  oi 
(Castle  and  Forbes,  1906);  and  (3)  when  spotted  guinea-pigs  or  rats 
crossed  with  those  not  spotted  (MacCurdy  and  Castle.  L907).     Davenport 
has  furnished  numerous  instances  of  the  same  thing  in  poultry;  indeed,  he  has 
shown  that "  imperfection  of  dominance  "  and  of  segregation  are  the  rule  rather 
than  the  exception  in  Mendelian  crosses  in  poultry."      I  astle,  L916d,  ; 

"  .    .       .  The  English  unit-character  had  changed  quantitatively  in  tra 
mission  from  father  to  son.    This  seems  to  us  conclusive  evidence  againsl 
the  idea  of  unit-character  constancy,  or  'gametic  purity."        I         •    and 
Hadley,  1915.) 

"...  .  We  are  often  puazled  by  the  failure  of  a  parental  type  to reappear 
in  its  completeness  after  a  cross— the  merino  sheep  or  the  fantail  pigeon,  for 


40 


AN   ANALYSIS   OF   THE   EFFECT   OF   SELECTION. 


example.  These  exceptions  may  still  be  plausibly  ascribed  to  the  inter- 
ference of  a  multitude  of  factors,  a  suggestion  not  easy  to  disprove ;  though  it 
seems  to  me  equally  likely  that  segregation  has  been  in  reality  imperfect." 
(Bateson,  1914.) 

Fractionation  is  referred  to  by  Bateson  in  this  same  paper  as  prob- 
ably due  to  imperfect  segregation.  Illustrations  are  Dutch  rabbit 
and  Picotee  and  other  sweet  peas.     (See  p.  298.) 

"Accordingly  we  seem  limited  to  the  conclusion  that  a  slowly  blending 
gene  is  involved  in  the  cross  between  early  flowering  and  late  flowering  peas, 
that  the  blending  after  one  generation  of  heterozygosis  may  be  small  in 
amount,  but  after  three  generations  it  is  in  the  majority  of  cases  practically 
complete,  so  that  the  commonest  '  constant '  class  in  the  entire  hybrid  popula- 
tion is  one  strictly  intermediate  between  the  modes  of  the  parental  varieties. 
This  interpretation  is  entirely  in  harmony  with  the  observed  modification 
through  crossing  of  many  Mendelizing  characters,  as  observed  by  Daven- 
port, Bateson,  and  many  others  in  poultry,  guinea-pigs,  swine,  and  other 
animals,  as  well  as  in  plants."     (Castle,  19166,  p.  215.) 

Hayes  (1917)  states  on  the  basis  of  his  experiments  with  variegated 
maize : 

" .  .  .  .  One  might  conclude  that  certain  heterozygous  combinations 
produce  germinal  instability  which  exhibits  itself  either  as  imperfect  segrega- 
tion, gametic  contamination,  or  sporophytic  variation." 

In  these  quotations  the  following  cases  have  been  cited  as  evidence 
in  favor  of  contamination,  and  therefore  calling  for  investigation  :l 


1.  Polydactyl  guinea-pigs  (Castle,  1906). 

2.  Long-haired    guinea-pigs     (Castle     and 

Forbes,  1906). 

3.  Spotted  guinea-pigs  and  rats  (MacCurdy 

and  Castle,  1907). 

4.  English  rabbits  (Castleand  Hadley,  1915). 

5.  Poultry,  plumage    and    toe    characters 

(Bateson  and  Davenport). 


6.  Merino  sheep. 

7.  Fantail  pigeons. 

8.  Dutch  rabbits. 

9.  Picotee  and  other  types  of  sweet  peas. 

10.  Flowering  time  in  peas  (Hoshino,  1915). 

11.  Unspecified  case  in  swine. 

12.  Variegated   pericarp  in  maize  (Hayes, 

1917). 


Before  we  can  discuss  some  of  these  cases  intelligently  it  is  neces- 
sary that  we  make  sure  what  Castle  means  by  the  terms  "gametic 
purity"  and  "unit-character."  Unless  these  terms  are  understood 
in  such  a  way  as  to  eliminate  from  consideration  the  idea  of  recombina- 
tion of  independent  factors  there  is,  of  course,  nothing  to  discuss. 
If  by  gametic  impurity  or  inconstancy  of  unit-characters  is  meant  that 
recombination  of  modifying  factors  occurs,  the  existence  of  such  phe- 
nomena must  be  granted  at  once — this  is,  in  fact,  the  main  contention 
of  the  school  of  "pure  line"  advocates  or  "mutationists."  I  think  the 
two  following  quotations  from  Castle  are  sufficient  to  show  that  there 
need  be  no  disagreement  on  the  question  of  defining  these  terms: 

"What  we  want  to  get  at,  if  possible,  is  the  objective  difference  between  one 
germ-cell  and  another,  as  evidenced  by  its  effect  upon  the  zygote,  and  it  is 

xThe  rough-coated  guinea-pig  wasfoimerly  cited  (e.g.,  Castle  and  Phillips,  1914),  but  is  now 
never  used.  This  is  because  Wright  (Castle  and  Wright,  1916)  has  shown  the  results  to  be  due 
to  multiple  factors. 


AN   ANALYSIS   OF   THE    EFFECT   OF    SELECTION.  I  1 

the  constancy  or  inconstancy  of  these  objective  differences  that   I  am  dis- 
cussing;.    If  these  are  quantitatively  changeable  from  generation  to  gem 
tion,  then  change  in  the  variability  of  the  zygote  composing  a  generation 
might  arise  without  factorial  recombinations."1     (Castle,  101  I 

"The  head,  the  hand,  the  stomach,  stomach-digestion,  these  are  not  unit- 
characters  so  far  as  any  one  knows.  But  if  a  race  without  hands  wen 
arise  and  this  should  Mendelize  in  crosses  with  normal  rates,  then  we  should 
speak  of  a  unit-character  or  unit-factor  for  'hands,'  loss  of  which  or  variation 
in  which  had  produced  the  abnormal  race.  But  in  so  doing  we  should  refer 
not  to  the  hand  as  an  anatomical  part  of  the  body  nor  to  the  thousand  ami 
one  factors  concerned  in  its  production,  but  merely  to  one  hypothetical  factor 
to  which  we  assign  the  failure  of  the  hand  to  develop  in  a  particular  >■ 
It  is  immaterial  whether  we  call  this  a  unit-character  or  unit-factor  or  use  both 
terms  interchangeably "     (Castle,  191G6,  p.  100.) 

1.    POLYDACTYL   GuiNEA-PlGS. 

The  most  extensive  data  on  this  case  are  apparently  in  the  paper 
(Castle,  1906)  cited  in  the  quotation  already  given.  The  extra-toe 
character  was  at  first  irregular  in  appearance,  but  wras  improved  by 
selection.  In  five  generations,  without  very  close  inbreeding,  a  practi- 
cally uniform  race  was  obtained.  When  crosses  to  normal  were  made, 
the  Fi  results  varied  from  nearly  all  normal  to  nearly  all  polydactylous. 
F2  contained  both  normal  and  extra-toed  individuals.  It  is  pointed 
out  by  Castle  in  this  paper  that  the  results  are  very  similar  to  those 
obtained  by  Bateson  from  polydactylous  fowls.  Bateson's  comment 
on  that  case  is  given  below. 

In  the  absence  of  any  definite  data  regarding  F2  counts,  the  case 
as  reported  is  entirely  explicable  on  the  multiple-factor  view.  Castle 
himself  said  of  it,  five  years  after  the  publication  of  the  above  paper: 

"An  alternative  explanation  is  possible,  viz.,  that  the  development  of  the 
fourth  toe  depends  upon  the  inheritance  of  several  independent  factors,  and 
that  the  more  of  these  there  are  present,  the  better  will  the  structure  be 
developed.  The  correctness  of  such  an  interpretation  must  be  tested  by 
further  investigation."     (Castle,  1911,  p.  101,  footnote.) 

So  far  as  I  have  discovered,  such  further  investigations  have  not 
yet  been  reported,  although  five  years  later  this  case  is  listed  as  No.  1 
among  those  that  demonstrate  contamination  of  allelomorphs. 

2.  Long-haired  Guinea-Pigs. 

The  reference  given  for  this  case  (Castle  and  Forbes,  1906)  seems 
to  contain  the  most  recent  and  complete  data  regarding  it. 

Angora  guinea-pigs  appeared  in  a  short-haired  stock,  apparently 
as  segregated  recessives.  On  crossing  to  short  and  extracting,  there 
were  produced  some  animals  of  intermediate  hair-length,  and  some 
unusual  ratios.  But  similar  intermediates  appeared  in  another  strain 
of  shorts,  apparently  uncrossed  with  angoras,  thus  making  it  highly 
probable  that  we  are  dealing  here  with  a  factor  already  present  in  the 

'Italics  mine. 


42  AN   ANALYSIS   OF   THE   EFFECT   OF   SELECTION. 

race,  and  not  produced  by  the  cross  of  angora  X  short.  The  unusual 
ratios  are  based  on  quite  small  numbers,  and  the  authors  admit  that 
there  are  difficulties  in  separation  of  the  three  classes,  apparently 
due  to  overlapping.  Moreover,  we  are  given  the  results  only  in  total, 
not  from  each  mating  separately. 

Castle  himself  has  said  of  this  case:  "  ...  a  single  unit-character 
is  concerned.  Crosses  in  such  cases  involve  no  necessary  change  in 
the  race,  but  only  the  continuance  within  it  of  two  sharply  alternative 
conditions."     (Castle,  1911,  p.  39.) 

3.  Spotted  Guinea-Pigs  and  Rats. 

The  reference  given  for  these  cases  is  MacCurdy  and  Castle  (1907). 
I  am  unable  to  find  in  that  paper  any  evidence  regarding  guinea-pigs 
that  bears  on  the  question  of  contamination.  Nothing  but  selection 
experiments  are  reported.  There  is,  so  far  as  I  am  aware,  no  evidence 
of  significance  in  this  connection  in  the  more  recent  literature  on 
spotting  in  guinea-pigs. 

The  evidence  referred  to  from  rats  is  apparently  that  obtained  from 
crosses  between  hooded  and  Irish  races.  Hooded  rats  extracted 
from  such  crosses  had  more  extensive  colored  areas  than  the  uncrossed 
hooded  rats.  The  data  given  by  Castle  and  Phillips  (1914)  and  ana- 
lyzed by  MacDowell  (1916)  show  that  this  is  true  only  when  the  hooded 
race  is  a  "minus"  one.  The  "plus"  hooded  race  becomes  less  pig- 
mented when  crossed  to  Irish  (or  to  self).  MacDowell  has  shown  that 
these  results  conform  very  closely  to  the  expectations  based  on  the 
multiple-factor  view. 

The  later  evidence  on  the  case  of  the  hooded  rat  is  discussed  else- 
where in  this  paper. 

4.  English  Rabbits. 

The  data  for  this  case  are  contained  in  two  papers  (Castle  and 
Hadley,  1915a,  19156),  in  each  of  which  the  full  presentation  is  made. 
The  spotting  of  the  English  rabbit  is  a  dominant  character  and  is 
somewhat  variable.  A  single  heterozygous  male,  of  the  grade  desig- 
nated 2,  was  mated  to  a  number  of  Belgian  hares.  187  English  young 
were  produced,  of  mean  grade  2.43,  and  of  these  Fi  English,  a  buck  of 
grade  3.75  (only  one  Fx  English  was  of  higher  grade),  was  then  mated 
to  the  same  Belgian  hare  females.  189  English  young,  of  mean  grade 
2.92,  were  produced. 

This  case  presents  no  difficulties  for  the  multiple-factor  view,  since 
no  evidence  is  given  that  indicates  the  original  English  buck  to  have 
been  homozygous  for  all  modifying  factors,  or  that  prevents  us  from 
supposing  the  Belgian  mother  of  the  Fx  buck  to  have  transmitted  more 
plus  modifiers  to  him  than  were  present  in  his  father.  Under  the 
circumstances,  it  would  have  been  very  surprising  if  the  two  lots  of 
young  had  been  of  the  same  mean  grade. 


AN   ANALYSIS   OF   THE   EFFECT   OF   SELECTION.  13 

5.  Plumage  and  Toe  Characters  in  INm  i.thv. 

We  are  referred  to  the  observations  of   Iiat*->oii   and    Davenport 
for  these  cases.     In  one  instance  it  is  stated  that  Davenport  has  shown 
that  "imperfection  of  dominance"  and  of  segregation  are  the  rule  in 
poultry.    The  question  of  imperfection  of  dominance  is  noi  apro] 
in  this  connection.     As  Castle  has  said,  regarding  another 

"  ....  if  black  is  crossed  with  brown,  the  crossbreds  are  apt  to  develop 
in  their  coats  more  brown  pigment  granules  than  do  homozygous  or  pure 
blacks.  Nevertheless,  we  have  no  reason  to  question  the  entire  purity  of 
the  gametes,  both  dominant  and  recessive,  formed  by  such  cross-bred  black 
animals.  It  is  the  dominance,  not  the  segregation,  which  is  imperfei 
(Castle,  1911,  p.  91.) 

That  Fi  results  do  not  bear  on  the  question  has  been  shown  by 
Bateson  (1909),  who  says  with  regard  to  polydactylous  fowls: 

"It  might  be  pointed  out  that  when,  as  in  these  examples,  the  abnormal 
result  is  clearly  perceptible  in  F1;  no  question  arises  as  to  the  occurrence  of 
an  imperfect  segregation.  The  peculiarity  is  evidently  zygotic,  and  is  caused 
either  by  some  feature  of  zygotic  organization,  or  by  the  influence  of  external 
circumstances."  (Bateson,  1909,  p.  251.) 

Moreover,  in  any  case  involving  irregularities  in  dominance,  im- 
perfect segregation  in  crosses  between  different  breeds  would  be  very 
difficult  to  demonstrate. 

6.  Merino  Sheep. 

No  reference  to  the  data  in  this  case  are  given.  I  have  been  unable 
to  discover  anything  more  definite  than  a  few  general  statements  by 
practical  breeders  regarding  the  effects  of  crossing  Merinos. 

Bateson  admits,  in  the  passage  quoted  above,  that  this  and  the 
next  case  "may  be  ascribed  to  the  interference  of  a  multitude  of 
factors." 

7.  Fantail  Pigeons. 

This  case  has  been  studied  by  Morgan  (Morgan,  Sturtevant,  Muller, 
and  Bridges,  1915,  p.  186).  The  fantail  type  did  not  reappear  in  the 
comparatively  small  F2  generation,  but  individuals  not  far  from  the 
fantail  were  obtained;  and  when  the  Fi  hybrids  were  mated  to  fan- 
tails,  several  of  the  offspring  fell  within  the  range  of  the  fantail  r. 
Bateson's  "failure  of  a  parental  type  to  reappear  in  its  completen 
after  a  cross"  is,  then,  scarcely  applicable  to  this  case. 

8  and  9.  Dutch  Rabbits  and  Cases  in  Sweet  Peas.     Fractionation". 

These  are  the  specific  cases  cited  as  illustrations  of  Bateson's  theory 
of  "fractionation"  or  "subtraction  stages,"  of  which  lie  states  that 
'it  is  to  be  inferred  that  these  fractional  degradations  are  the  con- 
sequences of  irregularities  in  segregation."     In  the  ease  of  the  S\\ 
pea,  Bateson  has  pointed  out  that  white  flowers  and  the  extreme  dark 


44  AN   ANALYSIS   OF   THE   EFFECT   OF   SELECTION. 

flowers  of  the  deep  purple  Black  Prince  were  among  the  earliest  varia- 
tions to  appear,  while  the  intermediate  forms  have  arisen  later,  as  he 
suggests  by  fractionation.  It  would  seem  to  follow  that  they  have 
arisen  in  heterozygous  forms,  for  otherwise  the  fact  that  the  larger 
variants  appeared  first  would  be  of  no  significance.  There  is,  I  think, 
no  evidence  to  show  that  the  later  variations  did  actually  arise  in 
heterozygous  forms,  either  in  sweet  peas  or  in  rabbits.  These  factors 
are  all  inherited  separately,  and  this  fact  would  seem  to  rule  them 
out  of  consideration  if  one  adopts  the  chromosome  theory  of  inheritance 
or  if  one  appeals  to  multiple  allelomorphs  as  evidence  in  favor  of  the 
variability  of  genes.  In  short,  we  have  no  evidence  regarding  the 
origin  of  these  forms,  and  their  present  behavior  seems  to  indicate 
that  they  are  not  due  to  fractionation.  The  only  evidence  in  favor 
of  such  a  hypothesis  is  the  somatic  appearance  of  the  characters. 

10.  Flowering  Time  in  Peas. 
Castle  (1916a,  p.  324)  has  summarized  this  case  as  follows: 

"Hoshino  (1)  recognizes  that  gametic  contamination  results  from  cross- 
ing early  and  late  flowering  varieties;  (2)  recognizes  also  that  variation  may 
occur  among  the  cross-bred  families,  as  well  as  in  different  pure  lines  of  the 
uncrossed  races,  as  regards  the  'quality,'  value,  or  potency  of  the  same  gene; 
(3)  although  Hoshino  does  not  refer  to  the  fact,  his  observations  show  clearly 
that  genetic  variation  of  a  gradual  or  fluctuating  sort  occurs  in  at  least  one 
of  the  varieties  which  he  crossed. 

"  .  .  .  .  What  I  want  to  suggest  is  that  in  these  several  agencies  we 
have  a  sufficient  explanation  of  the  variation  observed  in  Hoshino's  F2,  F3, 
and  F4  generations,  without  invoking  a  two-factor  hypothesis  (as  Hoshino 
has  done),  one  factor  being  enough." 

Castle's  argument  is  that  a  difference  in  one  pair  of  genes  is  sufficient 
to  account  for  the  result,  if  contamination  be  assumed;  and  that  one 
difference  is  a  simpler  assumption  than  two.  I  have  argued  here  that 
such  an  assumption  is  not  simpler,  unless  we  can  find  positive  evidence 
that  contamination  ever  occurs.  In  the  present  case,  then,  we  must 
turn  to  the  evidence  that  led  Hoshino  to  suppose  contamination  to 
have  occurred. 

Hoshino  crossed  an  early-flowering  pea  and  a  late-flowering  one. 
The  Fi  was  nearly  as  late  as  the  late  parent;  F2,  obtained  by  self- 
fertilizing  Fi,  approximated  fairly  closely  to  3  late  :  1  early,  but  the 
two  classes  were  somewhat  more  variable  than  the  corresponding 
parent  varieties,  and  apparently  overlapped  slightly.  Hoshino  self- 
fertilized  236  of  these  F2  plants  and  obtained  46  families  that  he 
classified  as  constant,  i.  e.,  supposedly  homozygous.  This  is  a  fan- 
approximation  to  the  1  in  4  expected  if  two  pairs  of  genes  are  respon- 
sible for  the  result.  Hoshino  shows  that  two  pairs  of  genes  will,  in  fact, 
account  for  most  of  the  results  obtained.  There  are  certain  facts  not 
thus  accounted  for,  but  Hoshino  shows  (p.  265)  that  "secondary" 


AN   ANALYSIS    OF   THE    EFFECT    OF    SELECTION.  1~> 

modifiers  (i.  e.,  modifiers  producing  only  small  effects)  will  aeeounl 
for  all  these  facts,  with  a  single  exception.  Throe  families  wen  ob- 
tained from  F2  plants  that  must,  on  the  two-factor  view,  have  been 
of  the  same  constitution.  These  plants  were  heterozygous  for  one 
pair  of  genes  only.  They  produced,  in  F4(  the  Bame  type  of  later 
constant  (homozygous)  families,  but  differed  slightly  in  the  flowering 
times  of  the  earlier  constant  families  produced.  According  to  1 1  <  >- 
shino's  view,  if  the  earlier  types  differed  the  later  ones  should  have 
differed  in  the  same  direction,  because  they  must  have  received  the 
same  "secondary  modifiers."  This  objection  is  not  valid,  for  specific 
modifiers  that  act  only  in  the  presence  of  certain  other  genes  are  well 
known  (see  especially  Bridges,  1916),  and  are  sufficient  to  account 
for  the  differences  observed.  This  argument  is  the  only  one  that 
Hoshino  gives  to  support  his  conclusion  that  contamination  must 
have  occurred.  We  must  then  conclude  that  the  case  does  not  furnish 
positive  evidence  for  contamination,  since  it  is  explicable  without  re- 
course to  that  hypothesis.1 

11.  Unspecified  Case  in  Swine. 

This  case  is  cited  by  Castle  (19166,  p.  215),  but  no  references  or 
authorities  are  given.  It  appears,  however,  from  the  legend  under  fig- 
ure 93  (opposite  p.  139)  that  the  belted  character  is  the  one  referred  to. 
The  only  data  bearing  on  this  case  that  I  have  found  are  presented  by 
Spillman  (1907),  and  consist  of  information  supplied  largely  by  prac- 
tical swine-breeders.  Spillman  himself  interpreted  the  case  as  one  in 
which  two  factor-pairs  are  involved.  The  data  also  suggest  the  pos- 
sibility that  we  are  dealing  with  a  case  of  " imperfect  dominance''  simi- 
lar to  those  in  poultry.     At  best,  the  data  are  meager  and  indefinite. 

12.  Variegated  Pericarp  in  Maize. 

The  paper  of  Hayes  (1917)  referred  to  above  should  be  studied 
in  connection  with  those  of  Emerson,  particularly  his  full  paper  (Emer- 
son, 1917),  dealing  with  the  same  character.  These  two  workers  have 
shown  that  there  is  a  remarkable  series  of  multiple  allelomorphs  in 
this  case,  and  Emerson  has  shown  very  clearly  that  some  of  these 
allelomorphs  mutate  quite  frequently — the  only  established  instance 
of  the  sort. 

'We  are  not  here  directly  concerned  with  Castle's  contention  that  Hoshino's  result*   pa 
the  effectiveness  of  selection  within  a  pure  line.     I  can  not,  however,  refrain  from  a  few  comments 
on  that  contention.     Castle  states  (1916a,  p.  324),  in  connection  with  the  differences  in  flowering- 
time  between  the  offspring  of  early  and  late  flowering  sister-plants:  "From  long  experience  in 
studies  of  rats  with  such  small  differences  as  are  here  indicated  I  have  no  hesitation  in  concluding 
that  fluctuating  variation  of  genetic  significance  is  here  in  evidence."     One  wonden  bo* 
perience  in  dealing  with  differences  in  pigmentation  in  rats  ran  give  an  observer  special  ability 
in  determining  by  inspection  the  significance  of  three-tenths  of  a  day  differ  ones  in  the  flowering 
time  of  peas.     With  respect  to  Castle's  calculations  from  Hoabino'l  data,  it  may  be  poii 
out  that  the  greatest  favorable  difference  recorded,  1.27  days,  is  inoorrect,  and  should  reed  0.26 
day.     In  view  of  the  fact  that  there  is  no  guarantee  that  the  material  Bead  *M  bomoeygoua, 
I  have  thought  it  scarcely  worth  while  to  recalculate  all  the  differences,  or  to  determine  their 
probable  errors;  but  it  is  certain  that  the  probable  error  of  each  difference  is  of  the  eame  order  of 
magnitude  as  the  average  difference  itself,  t.  c,  about  0.3  day. 


46  AN   ANALYSIS    OF   THE    EFFECT    OF    SELECTION. 

Hayes  has,  by  selection  from  a  mixed  population,  established  four 
different  grades  of  variegation  (including  self-colored  and  colorless) 
that  breed  true  and  that  represent  four  allelomorphs.  The  two  in- 
termediate types,  " mosaic"  and  "pattern,"  are  the  ones  of  special 
interest  in  the  present  connection.  When  these  two  types  were 
crossed,  the  mosaic  type  was  dominant,  but  there  was  an  increase  in 
variability  in  Fi  and  some  individuals  with  more  pigment  than  either 
parent  were  obtained.  The  parent  races  had  been  selfed  and  selected 
for  about  six  generations  before  the  cross  was  made.  In  view  of  the 
great  amount  of  heterozygosis  that  seems  to  be  normally  present  in 
maize,  and  the  large  number  of  chromosome  pairs  (20?),  this  seems  to 
be  hardly  sufficient  to  make  certain  that  both  races  were  pure  for  their 
modifiers.  The  increased  variability  of  Fi  is  therefore  not  surprising; 
and  that  phenomenon  would  of  course  be  expected  to  be  followed  by 
a  still  greater  increase  in  variability  in  F2.  Such  an  increase  was,  in 
fact,  observed,  and  is  the  chief  basis  for  Hayes's  conclusion  that  con- 
tamination may  occur.  The  data  are  not  sufficient  to  demonstrate 
that  new  allelomorphs  arise  more  often  in  heterozygotes  than  in  homo- 
zygotes;  and  even  if  it  be  shown  that  they  do  so,  it  does  not  follow  that 
there  has  been  contamination  of  allelomorphs.  There  are  too  many 
unknown  factors  involved  in  the  production  of  these  new  allelomorphs 
for  such  a  conclusion  to  be  valid  without  very  careful  controls. 

It  appears  from  the  foregoing  review  that  the  cases  cited  as  illustra- 
tions of  contamination  of  allelomorphs  or  imperfect  segregation  are 
all  explicable  on  the  multiple-factor  view,  or  rest  on  extremely  indefinite 
data. 

One  series  of  data  bearing  on  the  question  has  been  presented  in 
this  paper  (p.  32),  and  has  been  interpreted  as  giving  evidence  against 
contamination.  Three  other  cases  have  been  worked  out  by  Muller 
(1916)  and  Marshall  and  Muller  (1917).  Muller  kept  three  mutant 
characters  of  Drosophila  in  heterozygous  condition  for  about  75 
generations.  The  factors  were  kept  constantly  in  flies  heterozygous 
for  their  normal  allelomorphs,  so  that  the  characters  remained  unseen 
for  a  long  time.  s 

Muller  extracted  one  of  these  characters  (dachs)  from  this  stock, 
and  measured  the  tarsi,  using  the  length  of  thorax  as  a  standard  of 
comparison.  Dachs  flies  are  characterized  by  shortened  tarsi;  and 
the  flies  from  the  heterozygous  stock  were  found  to  have  tarsi  actually 
a  trifle  shorter  than  those  found  in  a  stock  that  had  been  kept  pure  for 
dachs.  This  result  was  not  very  conclusive,  chiefly  because  it  was 
based  on  a  very  few  flies. 

Marshall  and  Muller  made  much  more  extensive  studies  with  the 
wing  characters,  curved  and  balloon,  derived  from  the  same  heterozy- 
gous stock.     They  obtained  a  similar  result;  the  wings  were  no  nearer 


AN   ANALYSIS   OF   THE    EFFECT    OF    Mil  I    riON.  }7 

the  normal  than  were  those  of  curved  and  of  balloon  flics  thai  had  1 
kept  in  pure  stocks.    These  results,  taken  in  connection  with  the  d 
presented  above  for  bristle  number  in  flies  from  lines  heterozyg 
for  Dichaet,  furnish  definite  evidence  against  contamination  of  all< 

morphs  in  heterozygous  forms. 

Castle's  Experiments  with  Hooded  Rats. 

Perhaps  the  best  known  selection  experiment  is  thai  carried  oul  by 
Castle  and  various  collaborators  (Castle  and  Phillips,  1914,  Castle 
and  Wright,  1916,  etc.)  with  hooded  rats.  The  theoretical  conclu- 
sions reached  by  Castle  are  not  in  agreement  with  those  arrived  a1 
by  various  other  investigators,  including  the  author,  although  for  the 
most  part  the  data  obtained  are  very  similar.  Castle's  results  ha 
been  discussed  by  Muller  (1914a)  and  MacDowell  (1916),  who  ha 
shown  in  detail  that  all  the  data  known  to  them  were  explainable  on 
the  multiple-factor  view,  without  recourse  to  such  hypotheses 
contamination  of  factors  or  production  of  factorial  variations  by  selec- 
tion. One  point  has,  I  think,  not  been  sufficiently  emphasized  by 
them,  namely,  that  the  rat  experiments  are  hard  to  evaluate  properly 
until  we  are  in  possession  of  more  accurate  data  regarding  the  pedi- 
grees. Since  these  two  criticisms  were  written,  Castle  (Castle  and 
Wright,  1916)  has  given  some  additional  data,  which  he  has  used, 
in  a  reply  (Castle,  1917)  to  MacDowell's  paper,  as  arguments  against 
the  latter's  conclusions. 

With  regard  to  the  question  of  pedigrees,  to  take  up  these  ques- 
tions in  order,  the  main  point  on  which  information  is  desired  i-: 
How  closely  inbred  were  the  rats,  both  before  and  after  the  beginning 
of  the  selection  experiment?  The  following  quotations  contain  most 
of  the  available  evidence  on  this  matter: 

"Since  the  entire  stock  is  descended  from  a  very  few  individuals  (less  than 
a  dozen),  and  we  have  at  no  time  hesitated  to  mate  together  brother  and 
sister,  provided  they  varied  in  the  same  direction,  but  have  always  used  the 
most  extreme  individuals  (plus  or  minus)  which  were  available,  to  mate 
with  each  other,  it  follows  that  very  close  inbreeding  must  have  occurred 
throughout  the  experiment."     (Castle,  19146.) 

"It  is  impossible  for  a  colony  of  33,000  rats  to  be  produced  from  an  original 
stock  of  less  than  a  dozen  animals,  with  constant  breeding  together  of  tl 
which  are  alike  in  appearance  and  pedigree,  and  with  continuous  selection  of 
extremes  in  two  opposite  directions,  without  the  production  of  pedign 
which  in  the  course  of  each  selection  experiment  interlock  generation  after 
generation  and  finally  become  in  large  part  identical  with  each  other.     This 
has  been  repeatedly  verified  in  individual  cases,  but  is  incapable  of  a  n 
generalized  statement  or  of  demonstration  in  generalized  form.     At  least  I 
am  unable  to  devise  such  demonstration."     (Castle,  19164.) 

Elsewhere  (Castle  and  Phillips,  1914,  p.  20)  it  is  stated  thai  part 
of  the  original  stock  consisted  in  a  mixed  lot  of  trapped  rats  that  •hud 
probably  arisen  by  the  crossing  of  an  escaped  albino  rat  with  wild 


48  AN   ANALYSIS    OF   THE    EFFECT    OF    SELECTION. 

ones."  We  do  not  know  where  the  rest  of  the  stock  came  from,  and 
we  do  not  know  how  the  animals  used  to  start  the  selection  experi- 
ments were  derived  from  these  sources.  We  do  not  know  how  many 
individuals  were  used  to  start  the  selection  experiment ;  and  we  do  not 
know  anything  as  to  the  relationship  between  the  rats  in  the  two  series 
(plus  and  minus).  And,  finally,  we  have  only  very  indefinite  data 
as  to  what  system  of  breeding  was  followed  during  the  experiment. 
All  this  information  is  very  much  needed,  if  we  are  to  know  how  to 
interpret  the  results.  It  is  conceivable  that  each  series  was  split  up 
into  a  number  of  separate  lines,  and  that  these  have  been  crossed 
from  time  to  time.  Such  a  system  would  result  in  bringing  together 
modifying  factors  more  slowly  than  would  a  system  of  very  close  in- 
breeding. It  is,  of  course,  very  improbable  that  any  such  system  has 
been  followed;  and  such  an  assumption  is  by  no  means  necessary  for 
a  multiple-factor  interpretation  of  the  results.  But  definite  informa- 
tion is  very  desirable,  as  is  indicated  by  an  analogous  case. 

In  connection  with  certain  work  that  the  writer  has  been  carrying 
on  with  Mr.  J.  W.  Gowen,  pedigrees  of  the  two  famous  thorough- 
bred race-horses,  Sysonby  and  Artful,  have  been  tabulated.  These 
pedigrees  are  both  practically  complete  for  10  ancestral  generations. 
They  constitute  a  fair  random  sample  of  pedigrees  in  the  breed,  for 
Sysonby  was  of  pure  English  blood,  while  Artful  had  many  American- 
bred  ancestors.  The  two  pedigrees  show  no  name  in  common  until 
we  reach  the  fifth  ancestral  generation.  In  that  generation  there  are 
three  names  that  appear  in  both  pedigrees.  But  by  the  time  we  reach 
the  tenth  ancestral  generation,  approximately  90  per  cent  of  the  1,024 
names  in  Artful's  pedigree  appear  also  in  the  first  ten  generations  of 
Sysonby' s  pedigree.  And  the  result  would  certainly  be  even  more 
striking  if  the  pedigrees  were  studied  for  a  few  more  generations,  or 
if  two  English-bred  horses  were  compared.  Here,  then,  we  have  a 
clear  case  of  "interlocking"  pedigrees.  Yet  in  spite  of  the  long  in- 
breeding (12  to  20  or  more  generations,  with  scarcely  any  out-crosses) 
which  the  breed  has  undergone,  there  are  still  a  large  number  of  bay 
or  brown  and  of  chestnut  race-horses,  besides  a  few  grays  and  blacks. 
Of  the  four  Mendelian  factor  pairs  (see  Sturtevant,  1912)  for  which 
the  race  was  originally  heterozygous,  it  has  become  homogeneous  only 
in  that  the  roan  factor  has  been  eliminated.1  Clearly,  selection  for 
any  one  of  the  colors  now  present  would  still  be  effective  in  eliminating 
the  others.  The  breed,  which  we  may  suppose  to  be  inbred  to  some- 
thing like  the  same  degree  as  Castle's  hooded  rats,  is  still  very  far 
from  a  "pure  fine." 

The  new  data  presented  by  Castle  and  not  taken  up  by  MacDowell 
consist  of  two  points:     The  crosses  of  extracted  hoodeds  (from  plus 

1Even  in  the  early  days  roan  race-horses  were  not  at  all  common.     Both  roan   and  gray  have 
been  selected  against. 


AN   ANALYSIS   OF   THE    EFFECT    OP    BELEl    [TON.  \\l 

raceXwild)  to  wild,  and  the  relations  of  the  "  mutant  "  seriee  to  the 
selected  series. 

When  the  plus  race  was  crossed  to  wild,  and  F,  hoodedfl  were  ex- 
tracted, it  was  found  that  in  these  extracted  animals  the  mean  grade 
was  lighter  (less  "plus")  than  that  of  their  selected  grandparents. 
This,  as  MacDowell  pointed  out,  is  the  expectation  on  the  multiple- 
factor  view.     But  Castle  now  states  that  when  these  extracted  hoodedfl 
are  again  crossed  to  wild,  and  hooded  is  extracted  oner  more,  the 
twice-extracted  hoodeds  are  about  midway  in  mean  grade  between 
their  extracted  grandparents  and  the  uncrossed  plus  race.     As  he  Bays, 
the  wild  race  might  have  been  expected  to  bring  these  animal-  still 
farther  away  from  the  plus  race  if  modifying  factors  were  involved. 
Evidently  it  is  very  important  that  we  know  as  much  as  possible  about 
the  wild  rats  used  in  these  experiments,  in  order  that  we  may  know 
what  they  were  likely  to  carry  in  the  way  of  modifying  factors.     These 
rats,  we  are  told,  all  came  from  the  same  stock,  which  was  trapped  at 
the  Bussey  Institution  in  large  numbers  and  was  reared  for  two  gen- 
erations in  the  laboratory.     "In  making  the  second  set  of  crosses,  the 
extracted  individual  has,  wherever  possible,  been  crossed  with  its  own 
wild  grandparent."     An  examination  of  the  table  given  shows  that 
not  more  than  102  of  the  256  twice-extracted  hoodeds  can  have  been 
produced  in  this  way,  unless  individuals  of  the  same  sex  were  mated 
together.     Just  how  many  of  the  102,  and  which  ones,  does  "wherever 
possible"  include?     How  many  wild  rats  were  used  in  the  original 
crosses?     These  questions  are  important,  because  it  is  evident  from 
a  study  of  the  data  that  the  result  emphasized  by  Castle  is  due  almost 
entirely  to  the  descendants  of  one  original  plus-line  female;  41  of  the 
73  once-extracted  hoodeds  were  F2's  from  this  female;  and  their  mean 
grade  was  3.05,  as  against  3.3  for  the  remaining  F2's,  and  3.17  for  the 
generation  as  a  whole.     The  twice-extracted  hoodeds  tracing  to  this 
female  were  of  mean  grade  3.47,  while  those  from  the  other  original 
hoodeds  were  again  of  approximately  grade  3.3.     Further  data  re- 
garding the  pedigree  and  other  descendants  of  the  mates  of  this  female 
and  of  her  grandchildren  are  very  much  needed.     Information  regard- 
ing the  ancestry  of  the  female  herself  would  also  be  interesting. 

It  should  also  be  pointed  out  that  this  case,  accepted  at  its  face  value, 
is  difficult  to  explain  on  the  view  that  the  hooded-rat  results  are  pro- 
duced solely  by  variations  in  the  hooded  factor  itself.  On  that  view 
the  changes  brought  about  by  crossing  are  usually  referred  to  eon- 
tamination  of  the  factors  in  the  heterozygote.  But  that  interpretaf  ion 
leaves  entirely  unexplained  the  results  of  the  first  cross  to  wild.  If 
the  hooded  factor  is  contaminated  by  its  allelomorph,  the  onee- 
extracted  hoodeds  should  be  darker  than  their  grandparents,  wher 
in  reality  they  are  lighter,  as  would  be  expected  on  the  multiple-factor 


50  AN   ANALYSIS   OF   THE   EFFECT   OF   SELECTION. 

view.     Castle  has  met  this  objection  in  the  following  manner  (Castle 
and  Wright,  1916) : 

"This  suggests  the  idea  that  that  loss  (of  'plus'  character)  may  have  been 
due  to  physiological  causes  non-genetic  in  character,  such  as  produce  in- 
creased size  in  racial  crosses ;  for  among  guinea-pigs  (as  among  certain  plants) 
it  has  been  found  that  Fj  has  an  increased  size  due  to  vigor  produced  by 
crossing  and  not  due  to  heredity  at  all.  This  increased  size  persists  partially 
in  F2,  but  for  the  most  part  is  not  in  evidence  beyond  Fx.  I  would  not  sug- 
gest that  the  present  case  is  parallel  with  this,  but  it  seems  quite  possible 
that  similar  non-genetic  agencies  are  concerned  in  the  striking  regression  of 
the  first  F2  and  the  subsequent  reversed  regression  in  the  second  F2." 

This  comparison  seems  to  me  to  be  rather  far-fetched,  and  I  am 
quite  unable  to  understand  the  hypothesis  of  "  non-genetic  physiologi- 
cal causes."  That  they  are  "physiological"  is,  of  course,  obvious; 
but  they  depend  for  their  appearance  on  the  pedigree  of  the  animal, 
and  they  are  persistent  to  F2,  so  why  "non-genetic"?  The  results 
from  size  crosses  are  entirely  explicable  on  the  basis  of  Mendelian 
modifying  factors,  so  why  need  one  appeal  to  vague  "non-genetic," 
yet  transmissible,  factors?  And  is  not  such  an  appeal,  in  principle, 
an  appeal  to  modifying  factors?  It  certainly  involves  the  assump- 
tion that  the  grade  depends  on  transmissible  material  other  than  the 
hooded  factor  itself. 

In  the  tenth  generation  of  Castle's  plus  selection  series  there  ap- 
peared two  rats  of  considerably  higher  grade  than  any  individuals 
of  that  series  previously  recorded.  These  individuals  were  shown 
(Castle  and  Phillips,  1914,  pp.  26-31)  to  differ  from  the  plus  race  by 
a  single  dominant  factor.  This  has  been  taken  by  MacDowell  to 
indicate  that  a  new  modifying  factor  arose  by  mutation.  But  Castle 
has  now  presented  evidence  indicating  that  the  mutation  occurred 
in  the  hooded  locus  itself.  When  homozygous  "mutants "  were  crossed 
to  wild  rats,  F2  consisted  in  self-colored  rats  and  rats  of  the  same  grade 
as  the  mutant  series — no  hooded  individuals.  (Castle  and  Wright, 
1916.)  Castle  (1916)  concludes  from  this  evidence:  "This  serves 
to  confirm  the  general  conclusion  that  throughout  the  entire  series 
of  experiments  with  the  hooded  pattern  of  rats  we  are  dealing  with 
quantitative  variations  in  one  and  the  same  genetic  factor."  Now, 
the  "mutant"  variation  differs  from  the  other  results  obtained  by 
Castle  in  two  respects :  It  appeared  suddenly,  as  a  definite  and  very 
slightly  variable  character,  and  it  fails,  when  crossed  to  self,  to  give 
normal  hooded  in  F2.  Because  of  the  first  point,  it  is  probable  that 
it  arose  during  the  experiment  as  a  new  variation ;  because  of  the  sec- 
ond, it  is  probable  that  it  is  a  variation  in  the  hooded  factor  itself. 
Since  these  conclusions  as  to  its  nature  are  based  entirely  on  the  points 
in  which  it  differs  from  the  remainder  of  the  results,  it  is  difficult  to 
see  how  Castle's  case  for  these  results  is  in  any  way  improved.  On 
the  contrary,  if  this  is  the  behavior  to  be  expected  of  a  new  variation 


AN   ANALYSIS   OF   THE    EFFECT    OF    SELECTION.  .",  ] 

arising  in  the  hooded  factor,  then  the  "mutant  "  variation  a  evidently 

the  only  case  of  that  sort  that  Castle  has  reported. 

GENERAL  CONCLUSIONS. 

That  many  characters  may  be  influenced  by  more  than  one  pair  of 
genes  has  long  been  recognized,  and  this  is  the  essence  of  the  multiple- 
factor  view.  That  genes  exist  which  require  the  action  of  other  genee 
before  they  produce  visible  effects  has  also  been  long  known.  Kurt  her- 
more,  that  there  are  genes  which  produce  very  slight  visible  effects 
is  now  another  commonplace.  Given  these  three  facts,  and  the 
hypothesis  (which  is  supported  by  much  specific  evidence)  thai  m 
races  are  heterozygous  for  a  number  of  such  genes  is  all  thai  is  re- 
quired to  complete  the  conception  that  is  held  by  most  adherents  of 
the  view  that  multiple  factors  or  modifying  genes  are  responsible  for 
the  results  of  selection. 

In  specific  cases,  the  existence  of  definite  modifying  genes  has  been 
demonstrated  by  Dexter,  Bridges,  Muller  and  Altenburg,  and  the 
author.  All  other  data  in  question  fit  in  with  the  view  that  selection 
ordinarily  acts  only  by  isolating  modifiers. 

Modification  of  factors  by  selection,  crossing,  fractionation,  or 
similar  means  is  undemonstrated  in  any  given  case,  and  has  been 
shown  not  to  occur  in  other  cases  that  are  typical  of  the  results  usually 
obtained.  Factors  do  change,  and  more  than  two  forms  are  possible 
for  certain  loci;  but  there  is  no  known  method  of  inducing  such  changes, 
and  they  are  ordinarily  quite  rare  and  definite. 

SUMMARY. 

(1)  Dichset  is  a  dominant  character,  the  gene  being  lethal  when 
homozygous  (yellow-mouse  case).  The  gene  is  in  the  third  chromo- 
some. 

(2)  Dichset  flies  are  more  variable  in  bristle  number  than  are  not- 
Dichaets.     This  variability  is  partly  environmental,  partly  genetic. 

(3)  Selection  was  effective  in  isolating  both  plus  and  minus  Dicluel 
lines. 

(4)  A  cross  between  two  separate  inbred  plus  lines  gave  ao  increase 
in  variability  and  no  increase  in  parent-offspring  correlation.  There- 
fore the  two  lines  were  presumably  of  very  similar  constitution,  though 
independent  in  origin. 

(5)  A  cross  between  an  inbred  plus  line  and  an  inbred  minus  line 
gave  the  results  characteristic  of  such  crosses— increased  variability 
in  F2  and  increased  parent-offspring  correlation. 

(6)  Linkage  tests  demonstrated  thai  modifying  genes  exist   in  the 
selected  lines.     Several  lines  were  shown  to  differ  in  one  or  moi 
ond-chromosome  modifiers,  and  at  least  one  of  these  modifiers  v 
shown  to  cross  over  from  the  speck  gene. 


52  AN   ANALYSIS   OF  THE   EFFECT   OF   SELECTION. 

(7)  In  one  case  at  least  one  third-chromosome  modifier  was  shown 
to  exist  and  to  cross  over  from  Dichaet,  which  must  lie  to  the  left  of  it. 

(8)  Two  third-chromosome  lethals  were  obtained.  These  were 
shown  to  be  new  mutations,  not  due  to  fractionation  of  the  Dichaet 
gene. 

(9)  A  new  allelomorph  of  Dichaet,  called  Extended,  appeared  in  a 
plus  selected  line.  It  is  argued  that  this  mutation  was  not  due  to 
fractionation  of  the  Dichaet  gene,  and  was  not  influenced  by  the  selec- 
tion that  was  carried  on. 

(10)  Another  character,  somatically  indistinguishable  from  Ex- 
tended, was  shown  to  be  due  to  a  recessive  second-chromosome  gene. 

(11)  A  study  of  unselected  Dichaets,  and  of  the  not-Dicha3ts  pro- 
duced by  long-continued  mating  together  of  Dichaets,  is  shown  to  fur- 
nish evidence  against  the  view  that  allelomorphs  are  contaminated  in 
heterozygotes. 

(12)  A  general  discussion  of  the  selection  problem  is  divided  into 
three  parts:  (a)  an  attempt  is  made  to  clear  up  certain  current  mis- 
understandings and  disagreements  as  to  what  questions  are  really  at 
issue;  (b)  cases  cited  as  evidence  for  contamination  of  allelomorphs 
are  discussed  in  detail,  and  the  conclusion  is  drawn  that  contamina- 
tion is  unproved  and  is  an  unnecessary  hypothesis,  with  some  direct 
evidence  against  it;  (c)  certain  specific  objections  are  raised  to  argu- 
ments made  by  Castle  on  the  basis  of  his  experiments  with  hooded 
rats. 


BIBLIOGRAPHY. 

Bateson,  W. 

1909.     Mendel's  principles  of  heredity.     2d  impression,  Cambridge. 

1914.  Address  of  the  president  of  the  British  Association.     Science,  n.  s.,  40. 
Bridges,  C.  B. 

1915.  A  linkage  variation  in  Drosophila.    Jour.  Exper.  Zool.,  19. 

1916.  Non-disjunction  as  proof  of  the  chromosome  theory  of  heredity.     Geneti< 
Calkins,  G.  N.,  and  L.  H.  Gregory. 

1913.     Variations  in  the  progeny  of  a  single  ex-conjugant  of  Paramecium  caudatum. 

Jour.  Exper.  Zool.,  15. 
Castle,  W.  E. 

1906.     The  origin  of  a  polydactylous  race  of  guinea-pigs.     Carnegie  Inst.  Wash. 

Pub.  49. 
1911.     Heredity  in  relation  to  evolution  and  animal  breeding.     New  York. 
1914a.  Multiple  factors  in  heredity.     Science,  39. 
19146.  Variation  and  selection;  a  reply.     Zeitschr.  Abst.  Vererb.,  12. 
1916a.  New  light  on  blending  and  Mendelian  inheritance.     Amer.  Nat.,  50. 
19166.  Genetics  and  eugenics.     Cambridge,  Mass. 
1916c.  Report  in  Carnegie  Inst.  Wash.  Year  Book  No.  15. 
1916d.  Can  selection  cause  genetic  change?     Amer.  Nat.,  50. 

1917.  Piebald  rats  and  multiple  factors.     Amer.  Nat.,  51. 
and  A.  Forbes. 

1906.     Heredity  of  hair-length  in  guinea-pigs  and  its  bearing  on  the  theory  of  pure 
gametes.     Carnegie  Inst.  Wash.  Pub.  49. 

and  P.  B.  Hadley. 

1915a.  The  English  rabbit  and  the  question  of  Mendelian  unit-character  constancy. 

Amer.  Nat.,  49. 
19156.  Same.     Proc.  Nat.  Acad.  Sci.,  1. 
and  J.  C.  Phillips. 


1914.     Piebald  rats  and  selection.     Carnegie  Inst.  Wash.  Pub.  195. 
and  S.  Wright. 


1916.  Studies  of  inheritance  in  guinea-pigs  and  rats.     Carnegie  Inst.  Wash.  Pub.  241 . 
Dexter,  J.  S. 

1914.  The  analysis  of  a  case  of  continuous  variation  in  Drosophila  by  a  study  of  its 

linkage  relations.     Amer.  Nat.,  48. 
Emerson,  R.  A. 

1917.  Genetical  studies  of  variegated  pericarp  in  maize.     Genetics,  2. 
Hayes,  H.  K. 

1917.     Inheritance  of  a  mosaic  pericarp  pattern  color  of  maize.     Genetics,  2. 
Hoshino,  Y. 

1915.  On  the  inheritance  of  the  flowering  time  in  peas  and  rice.     Journ.  Coll.  .Wr. 

Tohoku  Imper.  Univ.,  Sapporo,  Japan,  6. 
Jennings,  H.  S. 

1916.  Heredity,  variation,  and  the  results  of  selection  in  uniparental  reproduction 

in  Difflugia  corona.     Genetics,  1. 
Johannsen,  W. 

1903.     Ueber  Erblichkeit  in  Populationen  und  in  reinen  Linien.     Jen*. 
Little,  C.  C. 

1915.     The  inheritance  of  black-eyed  white  spotting  in  mice.     Amer.  Nat  .  1'. 
Ltjtz,  F.  E. 

1911.     Experiments   with   Drosophila   ampelophila   concerning   evolution.     Cari 
Inst.  Wash.  Pub.  143. 
MacCurdy,  H.,  and  W.  E.  Castle. 

1907.     Selection  and  cross-breeding  in  relation  to  the  inherit*!)  ^pigmente  and 

coat-patterns  in  rats  and  guinea-pigs.     Carnegie  Inst.  \\  a.-h.  Pub.  To. 

53 


54  BIBLIOGRAPHY. 

MacDowell,  E.  C. 

1915.  Bristle  inheritance  in  Drosophila.     I.  Extra  bristles.     Jour.  Exper.  Zool.,  19. 

1916.  Piebald  rats  and  multiple  factors.     Amer.  Nat.,  50. 

1917.  Bristle  inheritance  in  Drosophila.     II.  Selection.     Jour.  Exper.  Zool.,  23. 
Marshall,  W.  W.,  and  H.  J.  Muller. 

1917.     The  effect  of  long-continued  heterozygosis  on  a  variable  character  in  Droso~ 
phila.     Jour.  Exper.  Zool.,  22. 
Middleton,  A.  R. 

1915.     Heritable  variations  and  the  results  of  selection  in  the  fission  rate  of  Stylonychia 
pustulata.     Jour.  Exper.  Zool.,  19. 
Morgan,  T.  H.,  A.  H.  Sturtevant,  H.  J.  Muller,  and  C.  B.  Bridges. 

1915.  The  mechanism  of  Mendelian  heredity.     New  York. 
Muller,  H.  J. 

1914a.  The  bearing  of  the  selection  experiments  of  Castle  and  Phillips  on  the  variability 

of  genes.  Amer.     Nat.,  48. 
1914b.  A  gene  for  the  fourth  chromosome  of  Drosophila.     Jour.  Exper.  Zool.,  17. 

1916.  The  mechanism  of  crossing  over.     Amer.  Nat.,  50. 

1917.  An  Oenothera-like  case  in  Drosophila.     Proc.  Nat.  Acad.  Sci.,  3. 
Pearson,  K. 

1911.  On  the  probability  that  two  independent  distributions  of  frequency  are  really 

samples  from  the  same  population.     Biometrika,  8. 
Spillman,  W.  J. 

1907.     Inheritance  of  the  belt  in  Hampshire  swine.     Science,  n.  s.,  26. 
Sturtevant,  A.  H. 

1912.  A  critical  examination  of  recent  studies  on  color  inheritance  in  horses.     Journ. 

Genet.,  2. 


DETAILED  DATA. 
Table  25. — Inbred  Plus  Sum  s 


864  I. ink. 


Genera- 
tion and 
culture 
No. 

Parents. 

1 

2 

3 

4 

5 

0 

7 

B 

1 

Grade. 

Cul- 
ture. 

9 

& 

9 

<? 

9 

cf 

9 

l10 

4 
5 

5 

g 

9 

d" 

9 

d 

9 

d 

• 

c* 

9 

& 

Fj  893 

F2  902 
903 

F3  926 

F4  1006 
1013 

Ffi  1064 
1081 
1084 

Ffi  1153 

6  1170 
1191 

F7  1239 
1277 
1287 
1298 
1299 
1309 
1318 
1322 

F8  1384 
1390 
1406 
1420 
1421 
1422 
1430 
1431 
1444 
1459 
1478 

Fo  15H 
1576 
1613 
1629 
1690 

F10  1663 
1763 
1810 

F„  1887 
1890 
1944 
1963 
1982 

F12  2013 
2027 
2028 
2029 
2060 
2061 
2062 
2087 
2098 
2105 
2115 
2123 
21422 

6 

7 
7 

6 

6 
6 

6 
6 
6 

6 
6 
6 

6 
6 
6 
6 
6 
6 
6 
6 

6 
6 
6 
6 
6 
6 
7 
6 
6 
6 
6 

6 
6 
6 

7 
7 

6 
6 
6 

6 
7 
6 
6 

6 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

7 

6 
6 

6 

6 
6 

6 
6 
6 

6 
6 
6 

6 
6 
6 
6 
6 
6 
6 
6 

7 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

6 
6 
6 
6 
6 

6 
6 
6 

6 
6 
6 
6 
6 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

864 

»27 

5 

7 

7 

20 
26 

8 

7 

21 

2 
17 

3 
16 

9 
17 

4 

4 

13 

7 

3 

1 

4 

4 

16 

11 

10 

6 

3 

17 

6 

13 

_•: 

7 
4 
9 

1 

3 

16 

2 
10 
13 
20 

3 
14 
11 
12 

3 
9 
4 
5 
14 
6 
6 
5 
3 

17 
17 

32 

17 
28 

10 

7 

11 

4 

7 

21 

3 
16 
16 
22 

14 

16 

12 

5 

7 

2 

6 

5 

21 

38 

17 

3 

12 

6 

19 

5 
19 
19 

3 

7 

3 

4 

18 

24 

14 

16 

4 

6 

20 
17 
18 

17 
1-' 
17 

8 
11 

1 

i:. 
11 

8 
19 

17 
14 

28 

1-J 
21 

9 

7 
20 

6 

7 
21 

7 
16 
is 
18 
12 
19 
12 
12 

8 

7 

5 

4 

14 

35 

22 

4 

9 

7 

17 

4 

16 

24 

3 

7 

1 
11 
15 

11 

16 

5 

5 

5 

11 

25 
12 
18 

20 

12 

8 

9 
6 

7 
4 

1 
17 

•10 

113 

51 

70 

73 

26 

75 

12 
.'1 

-7 

17 
92 
88 

124 

88 

69 
60 

47 

22 
25 

24 
JJ 
95 
92 
mi 
21 
27 
13 
60 

15 
55 
53 
10 
21 

11 

37 

HI 

57 
58 
65 

95 
17 

n 

70 
65 

7 
50 

71 
44 

893 

903 

926 
926 

1006 
1013 
1013 

1064 
1081 
1081 

1153 
1170 
1191 
1170 
1170 
1170 
1191 
1170 

1239 
1277 
1277 
1298 
1298 
1299 
1287 
1309 
1287 
1287 
1298 

1390 
1421 
1459 
1444 

1478 

1511 
1613 
1613 

1763 
1763 
1810 
1810 
1810 

1887 
1887 
1890 
1890 
1887 
1890 
1890 

1NN7 

1944 
1887 
1944 
1963 

1887 

1 

1 
1 

1 

2 

1 

19 
25 

7 
1 
9 

23 
24 

6 

5 

1 
1 

4 

1 

8 

-' 

14 
6 

28 

20 

4 

19 

1 

l 

10 

8 
6 

1 
3 
4 
1 
13 
1 
3 
2 

6 
1 
5 

3 

1 

2 

16 

1 
2 

1 

1 

1 

1 

1 

2 

1 

1 

5 

2 
3 

1 

1 
2 

7 

1 
8 
1 
3 
2 

2 

18 

6 
9 

11 
5 
2 

11 

10 

3 
6 
7 
1 
5 

6 

7 

17 

10 
6 

14 
6 
6 

12 
3 
2 

16 
9 

If. 
1 

11 
5 

11 
3 
5 

1 

1 

1 

1 

4 

14 

4 
5 
7 
3 
3 

16 

1 
8 

4 
20 

2 
4 

7 
4 

1 

1 

l 

3 
2 

2 

1 

1 
1 

1 
1 
1 

2 

5 

14 

3 

1 
1 
1 

1 

7 

8 

in 

3 

4 

1 

7 
9 

4 

B 
6 

•l 

1 

4 

6 

13 

1 

1 
2 

Id 

1 

13 
5 
9 
6 
3 
2 

1 
1 

4 
4 

1 

1 

1 

1 

1 

- 

- 

'Offspring  not  separated  for  sex. 


•_M  l.roo.1  ,.f  . 


55 


56 


AN   ANALYSIS    OF   THE    EFFECT    OF    SELECTION. 


Table  25.— 

Inb 

RED 

Plus  Series. 

864  Line — Continued 

Genera- 
tion and 
culture 
No. 

Parents. 

1 

2 

3 

4 

5 

6 

7 

8 

"3 
o 
H 

Grade. 

Cul- 
ture. 

9 

cf 

9 

<? 

9 

cf 

9 

c? 

9 

<? 

9 

& 

9 

d" 

9 

& 

9 

c? 

F13  2132 
2144 
2146 
2167 
2180 
2219 
2221 
2241 

F14  2248 
2293 
2304 
2356 
2362 

7 
7 
6 
7 
6 
7 
6 
6 

6 

7 
6 
6 

7 

7 
7 
7 
6 

6 
6 

7 

7 

6 
6 

7 
7 
7 

2013 
2027 
2013 
2060 
2062 
2098 
2105 
2029 

2132 
2167 
2180 
2219 
2241 

1 

1 
1 

3 

2 
7 
6 
8 
3 
6 

1 

1 

8 
3 
6 

2 

8 

1 

3 

1 

4 

6 
19 
23 
20 
21 
16 
12 
14 

27 

14 

125 

9 

8 

6 
25 
17 
31 
13 
10 

2 
14 

25 
9 

12 
6 

15 
64 
53 
72 
44 
50 
18 
37 

60 

38 
28 
31 

18 

2 

2 

1 
3 
1 

3 

4 
2 
1 
2 
5 

4 
6 
ll 
2 
2 

2 

1 

2 
2 

1 

3 

8 

1 
2 

ll 

2 

1 

•••[•■• 

^The  original  record  sheet  for  2304  has  been  lost,  and  the  sexes  are  not  noted  separately  on  the 
copy  from  which  this  count  is  taken. 


Table  26.- 

—Inbred  Plus  Series 

.  1002  Line. 

Genera- 
tion and 
culture 
No. 

Parents. 

1 

2 

3 

4 

5 

6 

7 

8 

"3 

o 

Grade. 

Cul- 
ture. 

9 

& 

9 

d* 

9 

C? 

9 

C? 

9 

& 

9 

cf 

9 

<? 

9 

& 

9 

c? 

Fx  1072 

F2  H50 

1158 

F3  1213 
1233 
1247 
1264 
1278 

F4  1347 
1348 
1350 
1363 
1374 
1375 
1383 
1386 
1387 
1388 
1389 
1401 
1402 
1403 
1404 
1419 
1436 

F5  1479 
1494 
1498 
1502 
1509 
1513 
1516 

6 

6 
6 

7 
6 
6 
6 
6 

6 
6 
6 
6 
6 
6 
6 
7 
7 
6 
6 
8 
7 
6 
6 
6 
6 

7 
6 
6 
6 
6 
6 
6 

6 

6 
6 

6 
6 
6 
6 
6 

8 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
7 
7 
6 
6 

6 
6 
6 
6 
6 
6 
6 

1002 

1072 
1072 

1150 
1150 
1158 
1150 
1150 

1213 
1213 
1247 
1213 
1247 
1247 
1213 
1264 
1264 
1247 
1247 
1213 
1213 
1233 
1264 
1264 
1264 

1350 
1347 
1350 
1347 
1363 
1389 
1404 

•  •  • 

20 

5 
35 

4 

14 

11 
30 

1 

17 

15 

11 

14 

2 

6 

3 

24 

17 

16 

34 

4 

6 

11 

3 

10 

5 

5 

1 

6 

8 

1 

1 

20 

6 

17 
6 
5 

18 
6 

17 
8 

21 

17 

12 

20 
1 

11 
5 

20 

16 
6 

13 
5 
6 

12 
9 
5 
5 

18 
1 

17 
4 
6 
5 

12 
5 

7 
5 

14 
9 
3 

15 
3 

16 

42 
11 

32 
16 
24 
37 
14 

39 

12 

12 

7 

17 

23 

16 

2 

3 

6 

5 

19 

14 

22 

24 

42 

22 

14 
21 
18 
36 
39 
13 
50 

26 

30 
10 

46 
11 
29 
33 
22 

27 

9 

12 

4 

13 

16 

13 

9 

3 

8 

5 

21 

9 

25 

22 

35 

16 

24 
27 
30 
45 
36 
23 
44 

114 

121 
110 

120 
32 
80 
84 

130 

122 
73 

163 
27 
72 

106 
44 
44 
36 
79 
14 
86 
46 
56 
54 

125 
52 

77 
63 
76 

127 
93 
98 

116 

1 

1 

1 

2 

1 

1 

5 

2 
22 

11 

16 

54 

4 

14 

22 

3 

9 

7 

21 

2 

15 

6 

1 

1 

9 

9 
2 
5 

11 
2 

17 
1 

5 

1 

28 

11 
11 
33 
1 
14 
17 

9 

7 
15 

8 
4 
1 

6 
2 

6 

4 
4 

1 
13 

1 

2 

1 

1 

1 
1 

1 
3 
1 
1 

2 

2 

1 

1 

3 

1 

1 

1 

4 
5 

1 

1 

1 

1 

2 

4 
4 

2 

6 

3 

AN   ANALYSIS   OF  THE   EFFECT   OF   SELECTION. 


57 


Table  26.— Inbred  Plus  Series.     1002  Link— Gontinoed. 


Genera- 
tion and 
culture. 
No. 

Parents. 

1 

2 

3 

4 

6 

', 

7 

9 

i 

0 

- 

Grade. 

Cul- 
ture. 

9 

c? 

9 

<? 

9 

cf 

9 

1 
1 

7 
1 

9 

6 

12 

0* 

13 

2 
3 
5 

9 

30 
32 
15 
25 

7 
19 
33 
21 

12 

15 

14 

9 

8 
17 
L".t 
12 
20 
17 
17 

9 

25 
8 
13 
14 
25 
16 

19 

10 

7 
10 

7 

9 
15 
19 

7 
18 
13 

14 
27 
17 
15 
13 
5 
8 
17 
24 

32 
in 
M 
26 
13 

34 
11 

8 

27 

12 
23 
5 
26 
26 
10 

3 
14 
11 
17 

4 
22 
22 

9 
20 
15 
13 
11 

20 
10 
14 
14 

19 

18 

22 

6 

8 

10 

7 

7 

15 

10 

17 

11 

19 

12 

7 
14 
14 

6 
15 

4 

5 
14 
23 

32 

13 

81 

27 
16 

n 

7 

9 

1 
4 
1 
3 
3 
1 
3 
4 

2 

1 

9 

<r 

9 

d1 

FB  1529 
1539 
1540 
1543 
1546 
1549 
1556 
1558 

F.  1611 
1637 
1644 
1671 
1679 
1680 
1681 
1692 
1694 
1712 
1731 
1734 

F,  1788 
1803 
1811 
1830 
1831 
1870 

F„  19121 
19981 
1913 
19241 
19991 
1939 
1945 
1949 
1974 
1976 
1977 
2000 

F9  2036 
2096 
2101 
2116 
2117 
2129 
2130 
2134 
2147 

F10  2199 
2231 
2232 
2247 
2308 

Fn  2338 
2354 
2389 

6 
6 

7 
6 
6 
6 
6 
6 

7 

7 
6 

7 
7 
7 
7 
7 
7 
7 
7 
6 

7 
7 
7 
6 
8 
6 

6 
6 
6 

7 
7 
6 
7 
6 
7 
7 
7 
6 

7 
6 
6 
6 
6 
6 
6 
6 
7 

6 
6 
6 
6 
6 

6 

7 
7 

6 
6 
6 

6 
7 
6 
6 
6 

6 
6 
6 
6 
6 
6 
6 
7 
6 
6 
7 
6 

6 
6 

7 
7 
7 
6 

7 
7 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

6 
7 
6 
6 
6 
6 
6 
6 
6 

6 
6 

7 
6 

7 

7 
7 
6 

1387 
1403 
1402 
1401 
1348 
1375 
1403 
1383 

1502 
1509 
1494 
1494 
1539 
1546 
1546 
1556 
1558 
1558 
1516 
1498 

1611 
1679 
1692 
1692 
1692 
1731 

1788 
1788 
1788 
1788 
1788 
1788 
1811 
1831 
1811 
1830 
1830 
1870 

1939 
1977 
1912 
1945 
1974 
2000 
1977 
2000 
2000 

2096 
2129 
2117 
2134 
2147 

2199 
2232 
2247 

1 

87 
88 
81 
72 
17 
79 
BO 
38 

32 
37 
89 
28 
14 
50 
87 
29 
81 
79 
31 
75 

68 
18 
34 
33 
80 
41 

70 
12 
42 
25 
39 
21 
25 

116 
62 
35 

110 
27 

45 
52 
53 
37 

0 
51 
88 

50 

87 
29 
04 

56 

36 

3 

2 

11 

1 

1 

16 
2 
1 

3 

1 
16 

1 

2 
2 

11 

7 
7 
2 

3 

6 

17 

1 

10 
3 

7 

1 

20 

4 

2 

1 

1 

1 

2 
3 

1 

4 

2 
10 

4 
16 

1 
16 
12 

1 
3 

1 
3 

1 

1 
4 

11 
10 

3 
5 

10 
13 

1 

2 

1 

3 

11 

2 

10 
3 

20 
9 

11 

7 

1 

1 

1 

11 
3 

6 
2 

10 
2 
6 
1 
1 

21 
9 
4 

18 
1 

6 

7 
7 
8 
4 

2 

1 

16 

2 

11 
3 
2 
4 
5 
3 

16 
6 
4 

20 

5 
4 
8 
6 
6 

4 
3 

1 
5 

3 

3 

1 
1 
1 

13 
1 

5 

1 
8 
1 
4 
1 

1 

1 

3 

1 

1 

5 

1 

2 
1 
1 
5 

34 
4 
5 

17 

17 
6 
3 

12 

1 

1 

1 

1 

2 

3 

7 

2 

1 
8 

5 

1 
5 

1 

1 

9 

7 

12 

2 

9 

1 
1 
1 
2 
2 

8 
4 
2 

1 

1 
6 

1 

2 

1 

6 

12 

4 
1 

1 

1 

2 
1 
3 

2 

1 

1 

2 

11912  and  1998,  1924  and  1999,  represent  two  broods  from  tho  same  parents. 


58 


AN   ANALYSIS    OF   THE    EFFECT    OF    SELECTION. 


Table  27. — Inbred  Plus  Series.     1002  Line.     New  Set. 


Genera- 
tion and 
culture 
No. 

Parents. 

1 

2 

3 

4 

5 

6 

7 

8 

"c3 

O 

Eh 

Grade. 

Cul- 
ture. 

9 

d 

9 

o1 

9 

& 

9 

d" 

9 

d1 

9 

<? 

9 

d 

9 

d 

9 

d" 

2415 

F,  2423 
2424 

F,  2442 
"  2460 
2461 
2462 
2472 
2473 

F,  2496 
2503 
2517 
2531 
2547 
2548 

F4  2570 

F5  2654 

Ffi  2758 
2767 
2768 

F7  2851 
2866 

F8  2917 

Me 

7 
6 

6 
6 
6 
5 

7 
6 

6 
6 
6 

8 
7 
6 

7 

6 

6 

7 
7 

8 

7 

6 

LSS. 

6 
6 

6 

6 
6 
5 
6 
6 

6 

7 
7 
6 
7 
6 

7 

6 

6 
6 
6 

6 

7 

6 

About  F2 
from  2389 

2415 
2415 

2423 
2423 
2424 
2424 
2424 
2424 

2442 
2461 
2460 
2460 
2461 
2472 

2503 

2570 

2654 
2654 

2654 

2767 
2768 

2866 

1 

1 

8 

1 
1 

1 

1 

1 

1 
1 

2 
3 

6 

1 
1 

2 

5 
3 

1 

3 

24 

6 

2 

5 
2 

12 

4 
6 

2 

2 

3 

1 

3 
3 

29 

7 

7 

1 

3 
2 
4 

1 
6 

1 
5 

5 
6 

7 

2 

2 
3 
1 

1 
2 

35 

35 
35 

11 
46 
38 
47 
38 
39 

10 
30 
30 
13 
46 
27 

32 

24 

13 
28 
15 

17 
27 

29 

31 

40 
29 

6 
33 
35 
37 
37 
37 

9 
22 
35 
15 
39 
27 

35 

36 

12 

24 
18 

21 

19 

36 

1 

135 

89 

78 

20 
91 

80 
92 
78 
86 

22 
63 
87 
31 
104 
70 

79 

73 

28 
61 
39 

41 
51 

79 

3 

1 
2 
1 

4 
2 
2 

1 
5 
2 
2 
3 

l 

2 

1 

1 

2 
4 

1 

1 

1 

1 
4 

1 

1 
1 

1 

1 
1 

3 

1 

1 

4 

? 

Table  28. — Crossbred  Plus  Series. 


Genera- 
tion and 
culture 
No. 

Mother. 

Father. 

1 

2 

3 

4 

5 

6 

7 

8 

— 

-*> 
O 

H 

Grade. 

Culture. 

Grade. 

Culture. 

9 

d 

9 

1 

9 

d 

9 

d1 

9 

d 

9 

d 

9 

d  ? 

?  d 

F3  937 

F4  1040 
1041 
1045 
1067 

FR  1°74 
1090 
1099 
1100 
1101 
1115 
1116 
1144 
1145 

7 

6 
6 
6 
6 

6 
6 
6 
7 
6 
6 
6 
6 
7 

Stock1 

937 
937 
9261 
937 

10061 

1041 

1041 

1045 

1045 

1041 

1045 

1067 

1041 

6 

6 
6 
6 
6 

6 
7 
6 
6 
6 
6 
6 
6 
6 

9021 

937 

937 

10041 

937 

Stock1 

1041 

1041 

1041 

1045 

1041 

1045 

1041 

1045 

1 

1 
2 

2 

2 

3 

3 

40 

5 

26 

9 

8 
6 

10 

2 

9 

2 

1 

38 

3 

25 

4 

6 

10 

5 
1 
3 

4 

3 

4 

29 

16 

25 

2 

12 

11 

12 

9 

15 

1 

4 

9 

6 

3 

30 

15 

30 

15 

16 

19 

5 

17 

2 

6 

15 

22 
38 
35 
17 

34 
23 
34 
40 
31 
28 
27 
8 
17 

13 

21 
45 

22 

8 

31 
17 

30 
34 
28 
45 
23 
9 
15 

1 
1 
1 

1 
1 
2 
2 
3 

1 
1 

2  . 

3  '. 
1  . 
3  . 

.  1 

.  1 
.  21 

53 

58 

97 

198 

64 

172 

47 

107 

120 

111 

87 

98 

23 

47 

1Unselected,  or  from  inbred  plus  series. 

2This  is  probably  the  original  extended  mutant.     Not  included  in  totals. 


AN   ANALYSIS   OF   THE    EFFECT    OF    SELE<   i: 
Table  28.— Crossbred  Plus  Series    Continued. 


Genera- 
tion and 
culture 
No. 


Ffi  1129 
1130 
1131 
1146 
1151 
1171 
1187 
1188 
1190 
1196 
1197 
1204 
1227 

F7  H98 
1203 
1253 
1254 
1262 
1269 
1271 
1284 
1285 
1293 
1304 
1324 
1325 
1326 
1333 
1345 
1353 
13052 

Fs  1334 
1346 
1351 
1356 
1357 
1359 
1360 
1372 
1373 
13802 
1425 
1426 
1427 
1428 
1429 
1458 

F9  1457 
1492 
1496 
1497 
1501 
1538 
1541 
1612 


F101581 
1599 
1709 
1758 


Mother. 


Grade. 


6 
6 
6 

7 
6 

7 
7 
7 
7 
7 
6 
7 
6 


8 
7 
7 
8 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 

7 
7 
7 

7 

7 
7 
7 
7 

7 

7 
8 
7 


Culture. 


1045 

1074 

1074 

1074 

10721 

1099 

1090 

1101 

1101 

1100 

1115 

1116 

1101 


7 

1101 

7 

1130 

7 

1146 

7 

1129 

6 

1151 

7 

1171 

6 

1190 

7 

1188 

7 

1171 

7 

1190 

6 

1151 

7 

1204 

7 

1171 

7 

1171 

7 

1227 

7 

1227 

7 

1204 

NotD' 

1197 

1227 
1203 
1196 
1253 
1253 
1203 
1203 
1254 
1196 
1262 
1271 
1293 
1285 
1262 
1269 
1345 

1334 
1334 
1359 
1326 
1356 
1356 
1326 
1428 

1457 
1492 
1458 
1612 


Father. 


Grade 


6 
6 

7 
6 
6 

7 
7 
7 
7 
7 
6 
8 
6 

6 

7 
6 
6 
6 
6 
7 
7 
7 
6 
7 
7 
6 
6 
6 
6 
7 
8 

7 
6 

6 

7 
6 
6 

7 
(i 
7 
8 
7 
7 
7 
7 
8 
7 

7 
7 
7 
7 
6 
7 


7 
8 
7 
8 


Culture. 


1074 

1045 

Kill 

1074 

1081  > 

1090 

1100 

1100 

1090 

1100 

10811 

1090 

1115 

1131 
1099 
1131 
1115 
1144 
1129 
1131 
1171 
1190 
1151 
1187 
1171 
1227 
1190 
1188 
1190 
1227 
1090 

1203 
1204 
1203 
1227 
1203 
1204 
1227 
1204 
1254 
1090 
1304 
1304 
1284 
1293 
1293 
1285 

1345 
1351 
1346 
1356 
1333 
1360 
1357 
1  126 

1373 
1373 
L638 

153S 


s 

1 


6 
5 


2 

1 
6 

17 

7 


12 
14 


13 


7 
2 
3 

11 
5 


15 
6 


13 

11 

14 

2 

4 


1 

8 

15 


5 

17 

2 

10 
1 
9 

1 
5 
5 


9 

7 
8 

17 
11 


5 
5 
1 
1 

1 

5 

19 

1 
5 


24 


IS 

1 
1 


I  i 
16 

l 

I I 
1 
1 

Ki 

10 

3 

a 

4 
5 


2 
5 
2 
8 
3 
7 
7 
11 
5 
3 


7 
8 
6 

17 
9 


6 

4 
2 
6 

9 

13 

2 

3 


16 


1  I 

a 


16 
16 
22 

11 
48 
60 
26 
10 
40 
63 

26 
1 
22 
3 
24 
20 
8 
25 
20 
35 
13 
20 
28 
40 
14 
39 
38 
10 

41 

32 

5 

6 

is 

17 

6 

5 

19 

6 

39 

12 

20 

4 

L"< 

26 

1  t 

l 

48 

12 
16 

il 
18 

lit 


9 

17 

11 
25 
43 
12 

1  l 

53 

24 

8 
21 

5 

8 
23 
19 
24 
11 
23 
20 
18 
20 
34 
33 

9 

42 

22 
6 
9 

21 

16 
3 
r, 

17 

B 

15 
16 

1 

18 

1 
n 

1  » 
16 

21 

17 
13 

11 


: 


60 
M 

50 

76 

13 

78 

16 
68 

45 
20 
67 

77 
B3 

75 

35 

100 
92 

43 

148 
87 
12 

20 
57 
4  1 
12 

44 

124 

7 
71 

B 
160 

10 

20 

88 


•Unselected,  or  from  inbred  plus  series. 

2The  c?  in  these  cultures  also  was  the  father  of  1204. 


1305  is  not  tnoluded  i"  the  totals. 


60 


AN  ANALYSIS   OF   THE   EFFECT   OF   SELECTION. 


Tabi 

.E  29- 

-Inbred  Minus  Series. 

900  Line. 

Genera- 
tion and 
culture 
No. 

Parents. 

1 

2 

3 

4 

5 

6 

7 

8 

13 
o 

Gn 
9 

ide. 
c? 

Cul- 
ture. 

9 

cf 

9 

a" 

9 

<? 

9 

& 

9 

& 

9 

<? 

9 

J 

9 

c? 

F,  920 

922 

Fo  1007 
1008 

F,  1062 
1063 
1073 
1082 

F4  H34 

1135 
1149 

Ffi  I258 
1259 

1260 

1276 

1307 

F,  1391 
6  1415 

F7  1563 
1565 
1566 
1577 
1578 

Fa  1677 
1764 
1799 

F„  1850 
1862 
1928 
1930 
1973 

F10  1995 
2008 
2018 
2019 
2037 
2038 
2039 
2042 
2043 
2044 
2045 
2071 
2072 
2074 
2140 
2075 
2120 
2128 

F,,  2165 
2166 
2170 
2179 
2181 
2190 
2205 
2237 
2257 
2258 
2261 

4 
4 

4 
4 

4 
4 
4 
4 

4 
4 
4 

4 
4 
4 
4 
4 

4 
4 

4 
4 
4 
2 
3 

6 

4 
4 

4 
4 
4 
4 
4 

4 
4 
4 
5 
4 
4 
4 
4 
4 
4 
4 
4 
4 
4 
4 
4 
4 
4 

4 
4 
4 
4 
4 
4 
4 
4 
4 
4 
4 

4 
4 

4 
4 

4 
4 
2 
4 

4 
3 
4 

4 
4 
3 
4 
4 

4 
4 

2 
3 
3 

2 
3 

6 
4 
5 

4 
3 
5 

4 
3 

4 
3 
4 
4 
4 
4 
4 
4 
4 
4 
4 
4 
4 
4 
4 
3 
3 
3 

4 
4 
4 
4 
3 
3 
3 
2 
4 
4 
3 

900 
900 

920 
922 

1007 
1007 
1007 
1007 

1062 
1062 
1063 

1134 
1135 
1149 
1149 
1134 

1259 
1259 

1391 
1391 
1391 
1391 
1391 

1565 
1578 
1578 

1677 
1677 
1799 
1764 
1764 

1850 
1850 
1850 
1850 
1930 
1928 
1928 
1850 
1862 
1862 
1862 
1930 
1930 
1928 
1928 
1862 
1930 
1930 

2037 
2037 
2018 
2071 
2075 
2044 
2038 
2071 
2120 
2128 
2037 

23 

8 

26 
31 

21 
16 
26 

7 

7 

8 

10 

1 
18 
14 

3 

10 
1 

9 
2 
3 
3 

8 

6 
7 
1 

16 
14 
11 

23 
5 

6 
19 
14 

6 
19 
18 

5 

2 
15 
14 

9 
13 
12 
19 

16 
8 
4 

5 

1 
18 

1 
11 

3 

16 
10 

35 
20 

21 

13 

27 

4 

13 

8 

17 

1 

14 

6 

1 

10 

11 
6 

11 

19 

8 

18 
11 

7 
10 
19 

9 

15 
12 
15 

3 

17 

13 

6 

5 

7 
6 

5 

10 
9 

14 
11 

11 

8 

12 

5 

11 

8 
9 

5 
13 
7 
3 
5 

11 

7 

12 

12 
5 

18 
9 

7 

4 

1 

23 

2 

12 

14 

17 

13 

3 

7 

6 
15 

3 
4 

10 
3 

20 

8 
3 

7 
3 

3 
6 

2 

4 

12 

3 

14 

4 

4 

11 

12 

10 

2 

5 

3 
5 

4 
1 
3 

87 
43 

116 

88 

71 

52 

102 

31 

83 
43 
68 

36 
92 
64 
18 
33 

63 
40 

45 
7 
30 
13 
60 

43 
26 

7 

69 
51 
37 
91 
23 

30 
72 
48 
27 
81 
49 
33 
13 
69 
46 
45 
41 
38 
54 
10 
45 
33 
28 

39 
39 
67 
45 
43 
24 
21 
17 
17 
15 
13 

1 

1 

2 

1 

2 
1 

1 

1 
1 

1 
1 

1 

1 
6 

1 

5 

3 

1 

3 

1 
6 

9 
5 
1 

20 
11 

7 
23 

5 

9 

19 

23 

7 

18 

11 

8 

1 

17 

12 

14 

12 

10 

19 

1 

8 

2 

10 

5 
3 
18 
7 
3 
1 

4 

2 

13 

5 
2 
4 

17 
11 
10 
16 
5 

6 

13 
4 
4 

13 
8 
5 
2 

11 
6 
9 
5 
7 
3 
2 

10 
4 
4 

6 
8 
9 
6 
9 
2 
3 
5 
4 
4 
2 

7 

4 

10 

8 
6 
1 

6 

7 

3 

18 

2 

5 
10 
7 
5 
16 
7 
7 
2 
8 
6 
6 
4 
5 
9 
2 
6 
11 
5 

4 
10 
12 
5 
4 
5 
3 
2 
3 
2 
1 

3 

6 

2 

1 
1 

2 
1 

5 

4 
4 

7 
3 

1 
3 

3 
3 

2 

1 
2 

3 
5 

3 
1 

3 

1 
2 
1 

2 
7 
3 
5 
2 
10 
4 
3 
1 
1 
1 
4 

4 
4 

11 
5 
5 

11 

8 
4 
7 
6 
2 
5 
1 

2 
6 

1 

3 

4 

7 
2 
4 

4 

1 

1 
1 

1 

1 

1 
2 
3 
1 
3 

2 
4 
1 

8 
11 
5 
10 
8 
9 
8 
3 

1 

2 

3 

1 
4 

4 
3 

2 

1 
3 

3 

1 

AN   ANALYSIS   OF   THE    EFFECT   OF    SELECTION. 


61 


Table  30. — Inbred  Minus  Series,     si 


Genera- 
tion and 
culture 
No. 

Parents. 

1 

2 

3 

4 

5 

6 

7 

B 

1 

74 
L00 
100 

5 

68 

19 
65 

22 

Grade. 

Cul- 
ture. 

9 

cT 

9 

d" 

9 

(? 

V 

t? 

9 

c? 

9 

c? 

9 

cf 

9 

cf 

9 

o" 

Fj  884 

F2  898 

F,  923 
935 
936 

F4  1047 

F5  1H7 

1132 
F6  1257 

4 
4 

4 

4 
4 

2 

4 
4 

4 

4 

2 

4 
4 
4 

2 

3 
3 

4 

868 

884 

898 
898 
898 

935 

1047 
1047 

1117 

»1 

i6 

•I 

2 

1 
2 

2 
10 

14 

'38 

156 

32 
39 

1 

24 

8 
34 

8 

31 

22 

1 

18 

3 
10 

4 

»18 

•28 

10 
5 
1 

3 

6 
5 

11 
5 

1 

4 

8 

1 

•11 

e 

2 

i 

i 

2 

1 

1 

2 

7 

4 
1 

1 

1 

1 

3 

1 

2 

1 

1 

1 

3 
3 

1 

1 

•Sexes  not  separated  in  this  count. 


Table  31. — Crossbred  Minus  Series. 


Genera- 
tion and 
culture 
No. 

Mother. 

Father. 

1 

2 

3 

4 

5 

6 

7 

8 

i 

Grade. 

Culture. 

Grade. 

Culture. 

9 

(? 

9 

<? 

9 

t? 

9 

C? 

9 

16 
10 
21 

10 
9 
7 
9 
5 
9 

14 
4 
7 

10 
11 

3 
12 
11 
10 
12 
11 
14 
13 

6 

6 

10 
11 
17 

5 

21 
14 
11 

15 

11 
4 
6 

11 
9 

12 
4 
5 

10 

15 

1 

16 

10 

7 

6 

8 

9 

2 

5 

7 

17 

11 

S 

6 

; 
5 

8 
10 

2 
2 

2 
1 

9 

8 

1 
7 

9 

10 

1 

8 

1 

3 

1-. 

3 

10 

4 

0 
17 

8 
17 

9 

S 
6 
6 

4 
4 
2 
6 
1 
2 
1 
5 
2 

8 
2 
5 
in 
4 
1 
6 
3 

a 

5 

1 
7 
8 
6 

g 

V 

.' 

! 

:>" 

F4  1039 
1069 
1070 

FB  1087 
1093 
1094 
1125 
1136 
1140 
1155 
1156 
1159 

F6  H68 
1169 
1184 
1194 
1199 
1209 
1210 
1223 
1224 
1225 
1231 
1236 
1241 
1242 
1243 
1268 

4 
4 
4 

4 
4 
4 
4 
4 
4 
4 
4 
4 

4 
4 
4 
3 
4 
4 
4 
4 
4 
4 
4 
4 
4 
4 
3 
4 

J920 
1935 
1935 

1039 

1039 

1039 

1039 

1069 

10731 

1070 

1069 

1070 

10821 

1069 

1093 

1070 

1087 

1125 

1136 

1125 

1087 

1136 

1125 

1140 

1140 

1155 

1136 

1136 

4 
4 
4 

4 
2 
3 
2 

4 
3 
4 
4 
3 

4 
3 
3 
3 
3 
3 
3 
2 
3 
3 
3 
2 
4 
2 
2 

3 

1936 
1949 
*942 

1039 

1039 

1039 

10471 

10631 

10471 

10731 

1070 

10731 

1093 
1087 
1069 
1094 
1093 
1125 
1093 
1087 
1125 
1087 
1140 
1125 
1159 
1140 
1140 
1125 

1 

1 

2 

2 

7 

3 

1 

1 
1 

1 

3 
1 

4 

4 

1 

L2 

2 

19 

1 

2 

3 

1 
3 

1 
1 
1 

1 

l 
■l 

3  s 
28 
25 

59 
35 
3 
40 
36 
42 
10 
13 

11 
41 

1 
29 
22 
32 
10 

9 
21 
18 
12 
13 
27 
25 
11 

61 
11 
20 

43 

32 

6 

26 

27 
26 

7 
12 

3 

13 
31 

17 

20 

19 

9 

7 

28 

8 

21 

5 

13 

16 

3 

5 

1 

1 
1 

1 

150 
79 
94 

139 
97 
23 

103 
84 

123 
54 
41 
.'1 

61 
115 
11 
92 
69 
79 
80 

85 
48 
48 
48 

01 

so 

61 
34 

HJnselected,  or  from  inbred  minus  series. 


62 


Table  31. — Crossbred  Minus  Series — Continued. 


Genera- 

Mother. 

Father. 

1 

2 

3 

4 

5 

5 

7 

8 

tion  and 

culture 

No. 

Grade. 

Culture. 

Grade. 

Culture. 

9 

& 

9 

& 

9 

1 

9 
8 

9 

9 
21 

d" 

9 

d 

9 

d1 

9 

d 

o 

F-  1256 

4 

1168 

3 

1140 

16 

12 

17 

84 

'  1273 

4 

1125 

4 

1168 

1 

1 

8 

33 

18 

8 

13 

3 

12 

97 

1274 

4 

1168 

2 

1140 

2 

26 

25 

7 

12 

4 

4 

80 

1292 

4 

1199 

4 

1168 

1 

6 

61 

43 

14 

5 

1 

131 

1300 

4 

1194 

4 

1169 

2 

21 

13 

13 

12 

5 

4 

70 

1301 

4 

1169 

4 

1168 

4 

21 

13 

9 

6 

1 

1 

55 

1316 

4 

1194 

4 

1155 

7 

41 

34 

6 

9 

5 

2 

104 

1317 

4 

1209 

3 

1169 

1 

3 

18 

7 

1 

3 

1 

1 

35 

1321 

4 

1194 

3 

1199 

1 

3 

17 

16 

13 

4 

5 

5 

64 

1371 

4 

1194 

4 

1194 

2 

29 

30 

18 

9 

3 

5 

96 

1377 

4 

1243 

4 

1210 

1 

5 

30 

19 

4 

10 

2 

3 

74 

1393 

4 

1225 

4 

1210 

1 

2 

16 

16 

4 

3 

1 

43 

1395 

4 

1241 

4 

1243 

1 

3 

21 

16 

4 

1 

3 

2 

51 

1396 

4 

1242 

4 

1241 

1 

14 

15 

8 

2 

1 

1 

42 

1397 

4 

1236 

3 

1242 

20 

12 

8 

7 

5 

2 

54 

1410 

4 

1242 

3 

1242 

1 

39 

18 

13 

12 

4 

12 

99 

1411 

4 

1241 

3 

1242 

1 

10 

41 

27 

11 

5 

1 

96 

1412 

4 

1210 

4 

1224 

1 

4 

31 

21 

12 

11 

2 

82 

1433 

4 

1243 

4 

1268 

1 

6 

53 

26 

8 

14 

3 

5 

116 

F8  1413 
1414 

4 

1274 

3 

1223 

7 

6 

11 

7 

14 

11 

56 

4 

1292 

3 

1236 

18 

10 

8 

8 

3 

5 

52 

1434 

4 

1274 

4 

1274 

2 

10 

10 

5 

9 

7 

5 

48 

1441 

4 

1301 

3 

1292 

11 

16 

11 

6 

10 

9 

63 

1466 

4 

1317 

4 

1317 

1 

9 

15 

11 

4 

4 

2 

46 

1468 

3 

1292 

3 

1273 

5 

2 

4 

5 

3 

4 

1 

24 

1469 

4 

1292 

4 

1292 

6 

1 

2 

3 

2 

14 

1470 

4 

1274 

3 

1273 

1 

1 

19 

16 

5 

3 

4 

3 

52 

1475 

4 

1316 

3 

1316 

1 

14 

4 

9 

6 

6 

2 

42 

1476 

3 

1273 

3 

1321 

11 

12 

9 

10 

10 

10 

62 

1477 

4 

1316 

3 

1321 

6 

14 

13 

14 

7 

10 

1 

65 

1488 

4 

1301 

3 

1273 

29 

30 

10 

12 

6 

11 

98 

1490 

4 

1321 

3 

1292 

2 

20 

22 

13 

8 

5 

11 

1 

82 

1523 

3 

1321 

3 

1316 

1 

37 

61 

9 

7 

2 

4 

121 

1525 

4 

1377 

3 

1371 

2 

15 

32 

10 

10 

9 

3 

81 

1526 

4 

1301 

3 

1377 

18 

15 

9 

7 

1 

4 

54 

1531 

4 

1395 

3 

1301 

2 

40 

39 

12 

14 

1 

2 

110 

1532 

4 

1393 

3 

1395 

2 

9 

3 

3 

1 

2 

20 

1545 

4 

1393 

3 

1377 

1 

19 

16 

6 

3 

3 

4 

52 

1568 

4 

1395 

3 

1395 

1 

3 

62 

37 

17 

5 

7 

4 

136 

1570 

4 

1412 

3 

1412 

8 

31 

34 

19 

11 

2 

105 

1573 

4 

1433 

3 

1411 

1 

2 

12 

44 

28 

13 

13 

5 

2 

120 

F9  1666 
1668 

4 

1488 

4 

1488 

3 

50 

41 

8 

8 

3 

2 

115 

4 

1531 

3 

1523 

2 

2 

3 

3 

2 

4 

1 

17 

1669 

4 

1525 

3 

1531 

1 

9 

3 

3 

1 

17 

1687 

4 

1526 

3 

1525 

2 

20 

11 

9 

8 

10 

2 

1 

63 

1706 

4 

1525 

3 

1570 

2 

11 

10 

3 

3 

29 

1738 

4 

1523 

3 

1570 

1 

5 

6 

1 

5 

1 

1 

20 

1741 

4 

1573 

3 

1568 

5 

18 

11 

8 

5 

3 

1 

51 

1759 

4 

1545 

3 

1568 

1 

6 

29 

20 

3 

1 

2 

2 

64 

1779 

3 

1573 

3 

1573 

6 

6 

7 

5 

1 

25 

F101878 
1879 

4 

1666 

3 

1706 

1 

14 

18 

2 

3 

2 

40 

4 

1759 

3 

1706 

8 

14 

5 

9 

1 

37 

1881 

4 

1706 

3 

1741 

4 

2 

14 

11 

1 

2 

34 

1882 

4 

1666 

3 

1741 

2 

3 

17 

30 

5 

1 

1 

59 

1892 

4 

1759 

3 

1741 

3 

13 

13 

1 

2 

1 

33 

1917 

4 

1741 

3 

1759 

10 

11 

1 

2 

24 

1943 

4 

1779 

4 

1779 

1 

4 

16 

14 

1 

2 

38 

Fn2015 
2040 

4 

1878 

2 

1881 

.'5 

27 

38 

4 

2 

2 

1 

77 

4 

1943 

3 

1943 

5 

3 

2 

2 

12 

2051 

4 

1892 

2 

1882 

3 

8 

35 

20 

8 

3 

1 

78 

2076 

4 

1943 

3 

1943 

10 

4 

3 

3 

20 

2110 

4 

1943 

2 

1943 

5 

2 

2 

21 

20 

2 

5 

1 

58 

Fl22189 

4 

2051 

3 

2015 

4 

28 

33 

12 

10 

1 

6 

94 

2254 

3 

2110 

3 

2110 

2 

2 

6 

7 

11 

7 

1 

3 

39 

2272 

3 

2110 

2 

2110 

11 

14 

4 

4 

8 

3 

44 

AN   ANALYSIS    OF   THE    EFFECT   OF    SELECTION. 


Table  32 

■Speck  Minus 

I. INK. 

Genera- 
tion and 
culture 
No. 

Parents. 

1 

2 

3 

I 

5 

8 

7 

Grade. 

Culture. 

9 

J 

9 

J 

9 

■1 

9 
39 

34 

9 
17 

17 

9 

8 

■ 

9 

C? 

Fi  133l| 

4 

Not-D' 

1168   1 
Inbred  speck J 

F2  1465 
1487 
1507 

4 
4 
4 

4 
4 
3 

1331 
1331 
1331 

1 

22 
36 

18 
15 
31 

10 
12 
21 

12 
14 

211 

11 

10 

B 

6 

l.-. 
7 

1 

7  1 
12  1 

F8  1594 
1595 
1617 
1640 

1728 

4 
6 

4 

4 
4 

4 
4 
4 
4 
4 

1465 
1465 
1487 
1465 
1507 

2 

1 

11 
4 
2 

56 
21 
30 
30 
19 

51 
23 
19 
29 
17 

4 

7 

3 

10 

11 

2 
4 

1 

in 

6 

1 
2 
1 
6 
5 

1 
2 

1 
1 

128 

63 

59 

F4  1766 
1784 
1786 
1820 
1841 
1861 

4 

4 
4 
4 
4 
4 

4 
3 
3 
4 
4 
4 

1595 
1595 
1595 
1617 
1640 
1640 

f. 
1 
1 
6 

2 

45 
12 
11 
37 
24 
24 

48 
10 
13 
30 
23 
23 

4 

1 

4 

7 

12 

3 
3 

2 

7 

10 

2 

2 

1 

1 
2 

109 

7  1 
65 

7_ 

F5  1906 
19071 
19961 
1955 
1978 
1986 
2009 

4 
4 
4 
4 
4 
4 
4 

4 
3 
3 
3 
3 
4 
3 

1786 
1766 
1766 
1766 
1784 
1820 
1861 

1 

4 
1 
4 

3 
1 

22 
14 
27 
24 
22 
9 
14 

23 
23 
25 
13 
16 
11 
15 

1 

2 
3 

7 
2 

1 

1 
2 
3 
5 
4 
2 

1 

1 

47 
43 

51 
50 

-7 

31 

F6  2088 
2093 
2111 
2127 

4 
4 
4 

4 

4 
4 
3 
2 

1955 
1906 
1955 
1955 

1 

1 

5 

5 
1 

34 

11 
24 
11 

24 
14 
15 
13 

1 
1 
1 
4 

1 
1 

1 

65 

47 
31 

F7  2182 
2196 
2233 

4 
4 
4 

3 
4 
3 

2088 
2093 
2127 

1 

1 

10 

18 

9 

49 

20 

4 

43 

1 
3 

39 

14 
106 

F8  2348 

4 

2 

2233 

8 

11 

3 

4 

1 

27 

NEW  SET. 

2414 

F,  2431 
2432 

J 

4 

4 

lass. 

4 
1 

About  F2 
from  2348 
2414 
2414 

l 

1 

1 
1 

2 

18 

3 

7 

15 

2 
3 

5 

1 
1 

2 
1 

1 

41 

7 

n 

F2  2486 

4 

4 

2431 

1 

5 

16 

7 

5 

2 

36 

F,  2545 
2546 
2549 
2572 

4 
4 
4 
4? 

4 

4 

4 

24 

2486 
2486 
2486 
2486 

1 
2 
6 

10 

'.i 

14 

3 

16 

11 
'.' 

2 

3 

2 
3 

1 

1 

1 

1 

1 
1 

11 

F4  2596 
2601 
2603 
2606 
2631 

4 
4 
4 
4 
4 

3 
3 
3 
4 
3 

2545 
2546 
2549 
2545 
2549 

1 

l 
3 

4 

f. 
1 
3 

2(1 
17 
7 
10 
17 

22 
9 

10 
5 

8 

4 
3 
1 
2 
2 

2 
1 

1 

1 

21 

18 

F6  2663 

4 

2 

2603 

l 

2 

1 

f. 

2 

3 

1 

18 

F„  2760 

3 

1 

2663 

3 

1 

2 

1 

7 

F7  2S60 

4 

4 

2760 

5 

1 

1 

7 

!First  and  second  broods  from  same  pair. 

'Two  males  and  two  females;  the  same  flies  as  the  parents  of  2441  and  2  1 »'"-. 


64 


AN   ANALYSIS   OF   THE   EFFECT   OF   SELECTION. 


Table 

33. — Cross  of  Inbred  Plus  Lines. 

Genera- 
tion and 
culture 
No. 

Parents. 

1 

2 

3 

4 

5 

6 

7 

8 

r— ' 

oS 
9 
O 

Grade. 

Cul- 
ture. 

9 

c? 

9 

& 

9 

cf 

9 

d1 

9 

& 

9 

& 

9 

cf 

9 

cf 

9 

tf 

Fi  194l[ 

F2  2053 
2054 
2082 
2083 
2104 
2122 

5 

5 
Not-D' 
6 
6 
6 
5 

5 
6 
6 
5 
6 
6 
6 

17631 

1788/ 

1941 

1941 

1941 

1941 

1941 

1941 

2 
3 

3 

1 

21 
1 
3 

11 

1 

3 

2 
9 
2 

9 

2 
16 
10 

5 
14 

7 

4 

3 
6 

4 

7 

10 

8 

8 

12 
22 
10 
5 
20 
13 

18 

7 
6 
8 
6 
14 
4 

42 

25 
77 
33 
28 
81 
35 

1 

PLUS  SELECTED  SERIES. 

F3  2160 
2161 
2162 
2164 
2177 
2185 
2229 
2249 

F4  2280 
2282 
2287 
2298 
2301 
2314 
2317 
2332 
2355 

6 
6 
6 
6 
6 
6 
6 
6 

6 
6 
6 
6 

7 
6 
6 

7 
7 

8 
6 
6 
6 
6 
6 
6 
6 

6 
6 
6 
6 
6 
6 
8 
6 
6 

2053 
2053 
2053 
2054 
2053 
2083 
2104 
2122 

2177 
2160 
2162 
2160 
2185 
2164 
2177 
2229 
2249 

1 

1 

4 

2 

11 

7 

2 

6 
1 

3 

1 
1 

9 
6 
21 
32 
23 
14 
3 
20 

8 

3 

21 

15 

7 

7 

19 

21 

4 

16 
7 
24 
21 
16 
19 
12 
25 

15 

6 
17 
13 
11 

6 
16 
14 

7 

2 

2 

2 

32 

20 
79 
76 
43 
44 
18 
62 

28 
10 
40 
40 
18 
18 
44 
57 
15 

2 

1 

4 
4 

2 

2 

1 

3 

15 

8 
2 
6 

7 

2 

1 

1 

1 

3 
2 
1 

2 
1 

1 

1 

1 

2 

7 

1 

1 

2 
2 
9 
1 

1 

3 

10 

4 

1 

2 

MINUS  SELECTED  SERIES. 

F3  2178 
2197 
2198 
2212 
2250 
2251 
2262 
2271 

F4  2329 
2385 

Fj  2069J 

F2  2172 
2173 
2244 

F3  2279 
2284 
2285 
2330 
2331 
2403 

F4  2409 

Fj  I602J 

F2  1751 
1774 
1791 

4 
5 
4 
4 
4 
4 
4 
4 

5 
4 

5 

5 

7 
4 

7 
5 
6 
4 
4 
4 

7 
6 

6 
6 
6 

5 
5 
5 
5 
4 
3 
4 
3 

5 

5 

6 

5 

7 
4 

6 
4 
6 
4 
4 
4 

7 

6 

6 
6 
6 

2054 
2053 
2054 
2083 
2122 
2104 
2083 
2104 

2212 
2250 

19441 
1939/ 

2069 
2069 
2069 

2173 
2172 
2172 
2172 
2172 
2244 

2279 

14221 

1419/ 

1602 

1602 

1602 

1 

2 
1 

1 

1 

5 

1 

2 

1 
4 

1 

9 

4 
2 
3 

6 
1 

5 

1 

1 

3 

1 

0 
1 

3 
4 

1 

1 

4 
1 

1 
14 

2 
1 

18 
6 
6 
12 
17 
9 
7 
4 

6 

8 

15 

43 
37 

27 

17 
37 
39 
23 
29 
14 

12 

28 

6 
8 
9 

22 

8 

3 

13 

27 

11 

4 

4 

6 

7 

8 

37 
33 
17 

20 
39 
36 
20 
41 
13 

4 

25 

3 

6 

17 

2 
3 
2 

51 
20 
13 
31 
69 
21 
15 
11 

16 
17 

68 

124 

111 

73 

43 
96 
88 
58 
115 
33 

21 

82 

44 
27 
31 

1 
2 

1 

2 

1 

1 
1 

1 
1 

1 

1 

1 

1 
1 

8 

7 
5 
5 

4 
2 

6 

1 

8 

7 
4 

12 

17 

17 

8 

3 
2 

16 
3 

1 

7 

6 

4 

1 

12 

14 
15 
13 

5 
2 
1 
12 
2 

13 

11 
3 
2 

3 
4 
5 
3 
3 

1 
4 
2 
9 
1 

2 

2 

2 

1 

1 

1 

AN   ANALYSIS   OF   THE   EFFECT   OF   SELECTION. 


65 


Table  34. — Cross, 

Pli 

us  Line  X 

M 

Link. 

Genera- 
tion and 
culture 
No. 

Parents. 

1 

2 

3 

4 

5 

6 

7 

8 

0 

Grade. 

Cul- 
ture 

9 

cf 

9 

& 

9 

rf" 

9 

d* 

9 
1 

d" 

9 
4 

d" 

9 

3 

14 
16 
21 

1 
12 
15 
13 

2 

5 

3 

3 

4 

20 

1 

16 

10 

12 

13 

10 

9 

2 

19 

6 

37 

28 
28 
15 
11 
23 
23 
13 
16 
26 
35 
24 
9 
29 
24 
14 
51 

d" 

US 

5 

9 

6 

19 

29 
Ifi 

8 
12 
27 
20 

1 
25 
35 
33 
17 
11 
23 

8 

3 
40 

9 

<? 

9 

<? 

Fx  2939J 

295o[ 

F2  2999 
3004 
3008 

F,  3062 
3063 
3064 
3116 
3065 
3066 
3118 
3077 
3078 
3079 
3088 
3089 
3090 
3096 
3111 
3112 

6 
4 

6 
5 
4 

6 
3 
4 
4 
5 
6 
6 
4 
6 
4 
6 
3 
6 
5 
6 
5 

4 

6 

6 
5 
6 

6 
2 
3 
3 
5 
6 
6 
2 
6 
3 
6 
2 
6 
5 
6 
5 

2SG61 
2860/ 
28601 
2866/ 

2939 
2939 
2939 

3008 
3004 
3004 
3004 
3004 
3004 
3004 
3004 
3008 
3008 
3004 
3008 
3008 
3008 
3008 
3008 

1 

43 

10 

107 

70 
68 
86 
84 
61 
59 
24 
55 
74 

121 
48 
73 
81 
71 
38 

110 

5 
10 
14 

5 
26 
31 

1 
2 

15 
14 

8 
16 

20 

2 
14 
12 

2 

1 
2 

15 

12 
28 

2 
6 

19 

19 
5 
4 
3 
1 
5 

11 
4 

12 
5 

10 
4 
7 

1 

3 
8 

2 
1 

5 

4 

1 

2 

2 

2 

1 

1 

3 

2 

4 
1 

1 
1 

3 
3 

1 

2 

1 

9 

11 
1 

11 
9 

11 
2 

14 
3 
6 
2 
2 

1 

1 

1 

Table  35. — Reversed  Selection,  Minus  to  Plus. 


Genera- 
tion and 
culture 
No. 

Inbred 

gens. 

before 

reversal. 

Parents. 

3 

0 

H 

Grade. 

Cul- 
ture. 

1 

2 

3 

4 

6 

b 

V 

8 

9 

<? 

9 

0* 

9 

cf 

9 

0" 

9 

<? 

9 

? 

9 

<? 

5 

' 

V 

f 

900.     Inbred  Minus  Line. 

F3  1086 

2 

6 

6 

1007 

10 

13 

16 

13 

11 

5 

68 

F4  1175 

6 

6 

1086 

2 

7 

8 

14 

26 

13 

1 

71 

F5  1288 

•    • 

6 

6 

1175 

11 

4 

13 

14 

8 

5 

1 

56 

1289 



6 

6 

1175 

7 

5 

6 

4 

12 

7 

1 

ia 

868.     Inbred  Minus  Line. 

F4  1066 

3 

6 

5 

935 

7 

23 

16 

21 

22 

13 

10 

112 

F6  H42 
1143 

6 

6 

1066 

3 

13 

21 

12 

8 

13 

4 

74 

6 

6 

1066 

2 

9 

S 

9 

B 

6 

8 

50 

1157 

6 

6 

1066 

1 

1 

10 

17 

20 

21 

10 

ia 

101 

Speck   Minus  Line. 

F3  1627 

2 

6 

6 

1507 

60 

48 

25 

12 

9 

7 

161 

F    1783 
r*  1843 



6 
6 

6 
6 

1627 
1627 

1 
3 

8 
16 

11 
17 

2 
9 

10 

•l 

4 

•1 
2 

40 
51 

F5  1893 

6 

6 

1783 

1 

1 

4 

10 

3 

1 

1 

II 

Cultures  in  brackets  are  first  and  second  broods  from  same  pair. 


66 


Table  36. — Reversed  Selection,  Plus  to  Minus. 
864.      Inbred   Line. 


Genera- 
tion and 
culture 

No. 

Inbred 
gens, 
before 

rev  ersal. 

Parents. 

5 

6 

o 
H 

Grade. 

Cul- 
ture. 

1 

2 

.5 

4 

V 

8 

9 

c? 

9 

c? 

9 

c? 

9 

cf 

9 

c? 

9 

C? 

9 

d" 

9 

cT 

9 

C? 

Fll  1940 

10 

4 

5 

1763 

1 

6 

2 

6 

4 

10 

3 

1 

33 

Fi2  2089 
2125 

4 
4 

5 
3 

1940 
1940 

1 

1 

1 
3 

3 

6 

3 
4 

10 

4 

5 

7 

1 

20 
29 

Fl3  2269 

4 

4 

2125 

2 

12 

5 

22 

18 

2 

1 

62 

1002.     Inbred  Line. 

F5  1522 

4 

4 

2 

1375 

5 

4 

8 

13 

9 

22 

1 

62 

F6  1686 

4 

4 

1522 

2 

10 

13 

5 

5 

4 

7 

46 

F7  1816 

4 

4 

1686 

1 

7 

29 

17 

5 

4 

4 

1 

68 

F8  1958 

4 

3 

1816 

7 

4 

4 

4 

1 

2 

1 

23 

F7   19081 
19971 
1909 

6 
6 
6 

4 
4 

4 

3 
3 
3 

1734 
1734 
1734 

1 
1 

1 

4 
5 

1 

5 

17 

2 
3 

18 

3 
13 

1 

8 
10 

2 
5 

7 

5 

7 
6 

12 

37 
76 

New 
F4  2571 

16± 

5 

5 

2517 

1 

1 

4 

19 

22 

2 

49 

F5  2637 

6 

5 

2571 

4 

9 

13 

New 
F4  2583 
2629 

16± 
16± 

5 
3 

4 
5 

2547 

2547 

3 

2 

6 

1 

7 
6 

30 
11 

24 
8 

1 

73 
26 

'Two  broods  from  the  same  parents. 


Table  37. — Tests  for  Modifying  Factors.1 
900.     Inbred  Minus  Line. 


Genera- 
tion and 
culture 
No. 

Parents. 

Offspring 
characters. 

1 

2 

3 

4 

5 

6 

7 

+3 

O 

-H 

Soma. 

Stock. 

Culture. 

9 

cf 

9 

cf 

9 

c? 

9 

c? 

9 

(7 

9 

d1 

9 

cf 

1737     [ 
1937     | 
1970     [ 

4 
Sp 
Sp 

4 
Sp 

6 

900 

Sp 
Sp 

Sp 

1566 

1737 
1737 

2 

12 

11 

7 

6 

5 

12 

1 

56 

fNot-sp 

1 
1 

1 
4 
5 
9 

8 
10 
20 

8 

10 
3 
6 
2 

6 
3 
5 
5 

5 
4 
4 

1 

4 

1 
1 

35 
26 
41 
26 

\Sp 

fNot-sp 

\Sp 

1 

864.     Inbred  Plus  Line. 

1921     | 

2023  | 

2024  | 
2065     | 
2175     | 
20912   | 
21432    | 

2245     | 

Sp 

6 
Sp 

6 
Sp 

6 
Sp 

6 
Sp 

5 

6 
Sp 

6 
Sp 

6 
Sp  ro 

Sp 

864 

Sp 

Sp 

Sp 

Sp 

Sp" 
Sp' 

1331 

1763 

1921 

1921 

1921 

2023 
1921 

1921 

2065 
2127 

1 

4 

3 

8 
6 
4 
9 

2 
1 
14 
6 
8 
2 
1 
2 
7 
5 
4 
2 
5 
2 
2 
4 
3 

3 
7 
1 
7 
1 
1 
2 
4 
8 

2 
6 
2 

1 
2 

*7 

11 
6 
2 
3 
1 
3 
1 
4 

8 
2 
1 
5 
4 
3 
2 
4 

15 
6 

1 
6 
1 
6 

10 
3 
2 
5 
1 
3 

45 
35 
26 
32 
23 
15 
6 
45 
32 
30 
16 
20 
18 
16 
19 
13 
27 

fNot-sp 

\Sp 

fNot-sp 

1 

1 

1 

\Sp 

fNot-sp 

\Sp 

2 

fNot-sp 

17 
2 
6 
3 
5 
3 
2 
5 

2 

18 
3 
2 

\Sp 

12 
9 

4 
1 
3 
4 
5 
4 
9 

fNot-sp 

\Sp 

1 

1 

fNot-sp 

4 

\Sp 

fNot-sp  not-ro 
Not-sp  ro  .  .  .  . 

Sp  ro 

1 

3 
2 
3 
1 

1  In  tables  37  and  38  the  upper  row  in  the  parent  columns  refers  to  the  mother  of  the  culture  in 
question;    the  lower  row  to  the  father. 

2  2091  and  2143  are  two  broods  from  the  same  parents. 


AN  ANALYSIS  OF   THE   EFFECT   OF   SELECTION. 

Table  38.— Tests  for  Modifying  Factoid. 
864.     Inbred  Plus  Line. 


Genera- 
tion and 
culture 
No. 

Parents. 

Offspring 
charac- 
ters. 

1 

2 

3 

i 

5 

a 

7 

3 

H 
37 

Soma. 

Stock. 

Culture. 

? 

f 

9 

1 

9 

2 

9 

2 

4 

9 

cf    9     <f 
9    10     3 

0 

' 

1946     | 
2030     | 
2032     | 
2118     [ 
2086     | 
2218     [ 
2246     [ 
2372     { 
2374     | 

2376  { 

2377  | 

Sp 

6 

6 
Sp 
Sp 

5 
Sp 

2 

41 

62 

5 
Sp  se 

5 
Sp  se 

4 
Sp  se 

4 
Sp  se 
Sp   4 
Sp  se 
Sp   4 
Sp  se 

Sp 
864 

Sp' 
Sp 

Sp' 

1331 

864 

1331 
1331 
1331 
1331 
1331 
1331 

1763 
1946 

1946 

1946 
1955 
1887 
2086 
2088 
2086 
2127 
2246 
2233 
2246 
2233 
2246 
2233 
2246 
2233 

fNot-sp , 

\Sp 

1 

1 

3 
2 

7 

13 
15 

2 

28 

13 

14 

7 

1 

16 

6 
2 

4 

1 
1 

10 

7 
1 
1 
2 
1 
2 
15 

2  1 
1      1 
9      3 
1      2 

3  3 
1      1 
6      2 

45 

38 
17 
15 

'J 

4 

84 

fNot-sp 

\Sp 

fNot-sp 

fNot-sp 

ISp 

fNot-sp. 

ISp 

fNot-sp . 

ISp 

fNot-sp 

ISp 

Sp 

1 

1 

1 
1 

4 
13 
13 
21 
11 

7 
11 

8 

2 

5 
9 
9 
7 
11 
7 
7 
6 
3 

3 
1 
8 
3 
7 

1 

2 

4 

1 

6  .. 

1 

5 

2 

1  .. 

1 

17 
27 
39 
35 
40 
19 
20 
17 
18 

1      2 
2 
?, 

3      3 
1      2 

2  .. 

6 

1      3 

Sp.... 

1 

19 

14 

2 

7 

2      4 

49 

Crossbred  Plus  Line. 

1948     [ 
20783   | 
21413    | 

7 
Sp 
Sp 

4 
Sp 

4 

X  + 
Sp 
Sp 

Sp 

1758 

1948 
1948 

3 

6 

6 

3    1 

6      4 

38 

ISp 

fNot-sp 
ISp 

1 

2 
10 

5 
5 

3 

7 
5 

5 

1 

5    1 
3 

5      3 
3      1 
3      5 
2      2 

16 

7 

35 

28 

Crossbred  Minus  Line. 

2201     [ 
2382     | 
2131     [ 
2259     { 
2378     | 

2394  | 

2395  { 

2396  | 

2397  { 

Sp 
2 
5 

Spro 

4 

Sp 

Sp 

4 

5 

Sp 

Sp5 

Spro 
5 

Sp  ro 
5 

Sp  ro 
5 

Sp  ro 

Sp 
X- 

1331 
X- 

Sp 
Sp 

Sp' 
1331 
1331 
1331 
1331 

2051 
2201 
2182 
2015 

2131 
2259 

2259 
2233 
2259 
2233 
2259 
2233 
2259 
2233 

1 

2 

1 

3      3 

10 

fNot-sp 

ISp 

1 

2 
3 
1 

2 
5 

11 

2 

•1 

2 
2 

7 

5      6 
?, 

n 

ii 

20 

2      1 

fNot-sp . 

ISp 

fNot-sp 

ISp 

\Ro 

fNot-sp, 
ISp 

ISp 

|Sn 

l 

2 
2 

1 
2 

2 

2 

'.' 

9 

12 

13 

6 

11 

4 

5 

12 

13 

6 
5 
2 
8 
7 
3 

11 
5 

10 
4 

10 

9 
3 
4 
3 
3 

1 

3 

1 
1 

3 

3 
7 

1  .. 
7 

3 
4  .. 

2  .. 
1  .. 

3  .. 
3  .. 

5      4 

2      1 

1 

2  .  .. 

.   , 

23 
21 
20 
23 
81 
80 
13 
88 
is 

80 
80 

2  s 

2      1 
3 
1 
1 
3 
1 
1 
1 

sp  se  ro. 


ro. 


oludea  one  O  malt. 


68 


Table  38. — Tests  for  Modifying  Factoks- 
1002.     Inbred  Plus  Line. 


-Continued. 


Genera- 
tion and 
culture 
No. 

Parents. 

Offspring 
[characters. 

1 
9  <?  9 

2         3 

4 

5 

6 

7 

8 

"3 
o 
H 

Soma. 

Stock. 

Culture. 

<?  9 

f 

9 

tf 

9 

c? 

9 

& 

9 

& 

9 

<? 

2025     { 
2153     { 
2150     { 

2333     { 

2433     { 
2471     { 
2481     { 
2488     { 
2516     | 
2436     { 
2480     [ 
24751    [ 
251S1    { 
2476     { 
2519     { 
2607     { 
2669     { 

2698  j 

2699  [ 
2711     { 
2682     { 

2665     I 

27892   \ 
28032   \ 
2633     \ 
2690     \ 
2704     < 

2811     < 

6 
Sp  ro 
Sp  ro 
6 
5 
Sp 

5 
Sp  ro 

6 
2  spro 
Sp  ro 

6 

5 
Sp 

6 
Sp  ro 

5 
Spro 
Sp  se 

6 
Sp 

3 

4 
Sp 

4 
Sp 

5 
Sp 

5 
Sp 
Sp 

6 
Sp 

5 
Sp 

6 
Sp 

6 
Sp 

6 

6 
Sp 

5 

Sp  ro 

Sp  5 
Spro 
Sp   5 
Sp  ro 
Sp 

6 
Spro 

5 
Sp 

6 

5 

.  Spro 

1002 
1331 
1331 

1334 

1331 

1002 
1331 
1331 

'sP 

1331 

1331 

1331 

1002 

Sp 

Sp 
Sp 
Sp 

Sp 

Sp 

1002 

Sp 

Sp 

Sp 

Sp 

Sp 

1331 

1331 

1331 

Sp 

1002 

1331 

Sp 

1331 

1924 
1906 
2009 
2025 
2025 
1978 

2153 
2182 

2415 

2414* 

2431 

2433 

2433 

2433 
2432 
2471 
2432 
2414 
2415 

2436 
2436 

2436 

2436 
2436 

2548 

2607 

2607 

2607 

2607 
2607 

2607 
2596 

2669 
2663 
2711 
2663 

2570 
2601 
2633 

2633 

2704 
2663 

14 

7 

10 

7 

2 

10 

50 

1 

1 

9 

7 
12 
7 
3 
5 
4 
2 

4 
8 
5 
13 
8 
5 
6 
6 
3 

6 
9 
2 

6 
2 
5 
3 

12 

10 
8 
5 
1 
5 
1 
2 
2 

11 

4 
5 
2 

1 

1 

2 

1 

22 

7 
1 
2 

3 

1 

6 

2 

25 

1 

33 
40 
23 
27 
30 
13 
26 
18 
76 

ISp 

fNot-sp 

ISp 

1 

Not-sp  not-ro . 

Not-sp  ro .  .  . . 

Sp  not-ro 

Sp  ro 

[Not-sp 

3 

8 
4 
4 
12 
10 
16 
15 
15 

5 

10 

6 

4 

3 

8 

13 

5 

10 

9 
2 
8 
3 
2 
3 
3 
4 
11 

7 
1 
6 
6 
7 
4 

12 
5 

14 

5 

10 

14 

2 

2 
1 
4 

3 

2 
4 
5 
1 
1 

4 

1 

27 
24 

HO 
33 
49 

'38 
47 
31 
61 

[Sp 

1  . . 
.    3  .. 

2 

4 
2 
4 

1 

[Not-sp1 

1  . 

ISp 

[Not-sp 

1  . 

.    1  .. 

.    7  .. 

ISp1 

1  . 

[Not-sp 

ISp 

1 
2 

/Not-sp 

9 

6 

3 

5 

9 

13 

8 

9 

15 

10 

18 

10 

6 

1 
15 
14 
12 

7 
14 

8 
10 

2 
1 

1 

21 

8 
14 
17 
35 
37 
22 
21 
35 
28 
39 

\Sp 

2 
1 
6 

4 
2 

2 
1 

4 
1 

/Not-sp 

2 

2 
4 

\Sp 

4 
1 
3 

fNot-sp 

\Sp 

/  Not-sp 

ISp 

1 
1 
1 
3 

2 

4 

4 
1 
6 
2 

/Not-sp 

2 
3 

ISp 

1  .  . 

1 

/Not-sp 

2 
4 

2 
1 

2 
4 

3 
1 
4 
1 
3 
7 
6 
4 
5 
2 
5 
3 
11 
4 
4 
2 

13 

9 

13 

15 

3 

14 

10 

12 

10 

7 

2 

3 

6 

2 

14 

4 
8 
6 

16 

8 

17 

12 

11 

7 

15 

9 

12 

7 

2 

2 

2 
3 
6 
1 

2 
3 

1 
1 

1 
1 

1 

1 

34 
28 
32 
32 
17 
25 
27 
25 
35 
28 
23 
29 
19 
32 
21 
49 
13 
16 
12 

ISp 

1 

2 
1 

/Not-sp 

\Sp 

/Not-sp 

\Sp 

/Not-sp 

\Sp 

1 

3 
3 
6 
3 
6 
7 
6 
5 
1 

3 
2 
1 

7 

7 

5 
5 
1 
1 
1 

/Not-sp 

\Sp 

2 
6 
6 
6 
3 
1 
8 
2 

[Not-sp  not-ro. 
]  Not-sp  ro .  .  .  . 

1 

1 

2 
4 

1 
1 

1 

1  Sp  not-ro 

1  .  . 

Sp  ro 

1 

/Sp  not-ro 

\Sp  ro 

/Sp  not-ro 

\Sp  ro 

/Not-sp 

2 
2 
2 
3 

1 
6 
2 

1 

1 

4 

1 

10 

3 

8 

10 
6 
9 
6 
6 
4 
5 
1 

4 

8 
3 
4 
7 
1 
1C 

1 

1 

17 
13 
22 
13 
18 
34 
15 
23 

ISp 

1 

2 
1 
5 
1 
1 
1 

/Not-sp 

ISp 

Not-sp  not-ro. 
Not-sp  ro .  . .  . 

1  . 

5 
3 
2 

1  Sp  not-ro 

Sp  ro 

*2475  and  2518  are. Iwq  bloods  fro^r-  sa,iae  parents . 
■     »  \"  t  , 

'   !  North  tz 


!2789  and, 2803  had  the  same  male  parent. 


.  l-ibfary 


North  Carolina 


State  University  Librar.es 


S02776111 


